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See the Ugly Beauty That Lives in a Toxic Cave

Norman Pace collects samples of a microbial mat.
Microbiologist Norman Pace collects a sample of a brainy-looking mat made of microbes (called a vermiculation) that coats the ceiling of Sulphur Cave.
Photograph by Norman R. Thompson

Lurking below the quaint ski town of Steamboat Springs, Colorado, lies a cave belching deadly gases. Its ceiling is dotted with snottites, dangling blobs that look like thick mucus and drip sulfuric acid strong enough to burn holes through T-shirts. And the whole place is covered in slime.

So why would anyone want to go there?

“Being in the cave reminded me of being inside a huge organism—as if I had been swallowed by some gigantic, alien monster from deep in the ocean or from outer space,” says photographer Norman Thompson.

Thompson joined a small group of scientists who are among the few people to ever explore Sulphur Cave, and who found it eerily beautiful, and brimming with strange life. As shown in National Geographic’s exclusive video below, along with spiders and insects, the cave holds sulfur-breathing microbes and a new species of blood-red worm.

EXCLUSIVE VIDEO: Clumps of newly discovered blood-red worms thrive in Sulfur Cave, which contains levels of toxic gases so lethal that any human who enters unprotected could quickly die.

“In a sense, we really were inside of an organism,” Thompson says, “or perhaps more accurately, an ecosystem. Because the cave is a colony of organisms, living together in a lightless ecosystem, powered not by sunlight, but by the sulfur coming from deep within the Earth.”

Inside the Belly

To enter the 180-foot-long (54 meters) cave, the intrepid scientists had to squeeze into a pit entrance, a hole in the ground that skiers might glide right past. And if you happen to visit without special equipment, you ought to glide past. Otherwise, the cave’s gases could knock you unconscious in a jiffy.

“It’s sort of foreboding,” says David Steinmann, a cave biologist at the Denver Museum of Nature and Science. “You have to climb and crawl down a wet muddy slop that’s stinky and smells like rotten eggs.”

A snottite found in a sulphur cave.
Snottites are thick, mucus-like blobs formed by bacteria growing in a sulfur cave.
Photograph by Norman R. Thompson

“It’s belching toxic gases,” Steinmann says, “and in the winter you can see steam coming out. You have to stoop down and squeeze through to get into the first room. Once you’re in there, it’s totally dark.”

But when the team brought in lights, they found that the cave is also lovely, in its own way. Crystals made of gypsum glitter on walls, and a small stream washes across the floor. Long tendrils made of more microbial colonies wave in the water’s flow.

Thompson photographed the cave twice, entering only after scientists had aired out the crevice using large fans—appropriately, the kind normally used to flush out underground sewers. “Even with the poisonous air flushed out by the fan, the cave still stunk of sulfur,” he says.

Such sulfur-filled caves are rare, with some found in Mexico and Italy. The high levels of sulfur that create the gas in Colorado’s Sulphur Cave come from deep within the earth. The cave is formed in travertine, a type of stone formed by deposits from streams and mineral springs.

Hydrogen sulfide gas, which gives the cave its rotten-egg smell, can be deadly at high concentrations. Yet life thrives inside the cave despite both the hydrogen sulfide and carbon dioxide up to four times levels that could kill a human.

Wormy Wonders

The biggest surprise was the blood-red worms found in the cave. “There’s a hell of a lot of worms in there!” says Norm Pace, emeritus professor of microbiology at the University of Colorado Boulder.

Worms in Sulphur Cave, Steamboat Springs, Colorado. These worms are believed to live on the chemical energy in the sulfur in the cave, similar to the way tube worms live in a world without light at the bottom of the ocean. Also visible on the left side of the image are streamers—colonies of microorganism, similar to those seen in hot springs in Yellowstone National Park. Photograph by Norman R. Thompson
These worms in Colorado’s Sulphur Cave are believed to live on the chemical energy in the sulfur in the cave, similar to deep-ocean tube worms. On the left are streamers—colonies of microorganisms similar to those in hot springs in Yellowstone National Park.
Photograph by Norman R. Thompson

The small worms live clumped together on the cave floor, where they’re probably making a living by grazing on the bacteria growing in wet spots, Pace says.

They’re also intensely red, much like the famous Riftia worms found at deep-sea vents, which are also rich in hydrogen sulfide. Pace has studied life in the vents and expected the cave ecosystem to be similar. It wasn’t, exactly. The ocean worms have special structures called trophosomes filled with bacteria that are able to live on hydrogen sulfide; essentially they “breathe” it. The worms rely on the bacteria to do this, so Pace was surprised that so far, the team hasn’t found a special home for bacteria inside the Sulphur Cave worms.

As for the cave worms’ bright red color, it probably comes from high levels of hemoglobin and related compounds that protect the worm from hydrogen sulfide. Steinmann and his colleagues described the worms this year in the journal Zootaxa.

They named it Limnodrilus sulphurensis, in honor of the sulfur that powers the base of the food chain in this otherwise deadly environment.

“It took over a year for the sulfur smell to gradually air out from my cave coveralls,” Thompson says. But would he go back? He’s still drawn by its strange beauty he says, so yes— “in a heartbeat.”


Correction: The cave is 180 feet long, not deep. This has been updated, and I  deleted a sentence about organic matter in the cave’s travertine—the cave’s sulfur comes mainly from geothermal activity, with microbial breakdown of organic matter as an additional, but minor, source. A clarifying sentence has been added. —EE (updated 6/15)

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Butterflies Behaving Badly: What They Don’t Want You to Know

Small Grass Yellow butterflies feed on fresh elephant dung in Kenya's Tsavo West National Park.
Small grass yellow butterflies feed on fresh elephant dung in Kenya’s Tsavo West National Park.
Photograph by Nigel Pavitt, Getty

Butterflies have had us fooled for centuries. They bobble around our gardens, all flappy and floppy, looking so pretty with their shimmering colors. We even write odes to them:

Thou spark of life that wavest wings of gold,
Thou songless wanderer mid the songful birds,
With Nature’s secrets in thy tints unrolled
Through gorgeous cipher, past the reach of words,
Yet dear to every child
In glad pursuit beguiled,
Living his unspoiled days mid flowers and flocks and herds!
Ode To A Butterfly, by Thomas Wentworth Higginson

But butterflies have a dark side. For one thing, those gorgeous colors: They’re often a warning. And that’s just the beginning. All this time, butterflies been living secret lives that most of us never notice.

Take this zebra longwing, Heliconius charithonia. It looks innocent enough. 

The zebra longwing butterfly was made Florida's state butterfly in 1996.
The zebra longwing butterfly was made Florida’s state butterfly in 1996.
Pixabay, CC0

But it’s also famously poisonous, and its caterpillars are cannibals that eat their siblings. And that’s hardly shocking compared with its propensity for something called pupal rape.

Once you know that a pupa is the butterfly in its chrysalis—in between being a larva and an adult—then pupal rape is pretty much what it sounds like. As a female gets ready to emerge from her chrysalis, a gang of males swarms around her, jostling and flapping wings to push each other aside. The winner of this tussle mates with the female, but he’s often so eager to do so that he uses his sharp claspers to rip into the chrysalis and mate with her before she even emerges.

Since the female is trapped in the chrysalis and has no choice in the matter, the term pupal rape came about, though some biologists refer to it more charitably as “forced copulation” or simply pupal mating. Whatever you call it, it’s hardly the stuff of children’s books.

The zebra longwing is certainly pretty, though. Maybe that’s how it got to be Florida’s state butterfly.

And don’t think for a minute that zebra longwings are an anomaly—plenty of their kin are bad boys, too.

One day in Kenya’s North Nandi forest, Dino Martins, an entomologist, watched a spectacular battle between two white-barred Charaxes. A fallen log was oozing fermenting sap, and while a fluffy pile of butterflies was sipping and slowly getting drunk, the two white-barred butterflies showed up and started a bar fight. Spiraling and slicing at one another with serrated wings, the fight ended with the loser’s shredded wings fluttering gently to the forest floor.

A green-veined Charaxes dines on animal poop.
Photograph by Dino Martins

Martins, a former National Geographic Emerging Explorer, wrote about Charaxes, or emperor butterflies, in Swara magazine, published in East Africa where he is now Director of Kenya’s Mpala Research Centre.

“They are fast and powerful,” he writes. “And their tastes run to stronger stuff than nectar: fermenting sap, fresh dung and rotting carrion are all particular favourites.”

That’s right; don’t get between a butterfly and a freshly dropped pile of dung. It drives them wild. They uncoil their probosces and slurp away, lapping up the salts and amino acids they can’t get from plants.

It’s called mud-puddling, and it’s very common butterfly behavior. It doesn’t have to be dung, although that’s always nice; you may see flocks of butterflies having a nip of a dead animal (as depicted in this diorama of butterflies eating a piranha), drinking sweat or tears, or just enjoying a plain old mud puddle.

VIDEO: Did You Know Butterflies Drink Turtle Tears? Watch to find out why.

But still, butterflies are harmless, right?

Sorry, kids—not always. Butterflies start life as caterpillars, which are far from harmless if you’re a tasty plant, and can be carnivorous. Some are even parasites: Maculinea rebeli butterflies trick ants into raising their young. The caterpillars make sounds that mimic queen ants, which pick them up and carry them into their colonies like the well-to-do being toted in sedan chairs. Inside, they are literally treated as royalty, with worker ants regurgitating meals to them and nurse ants occasionally sacrificing ant babies to feed them when food is scarce. Butterflies invented the ultimate babysitting con.

So, let’s review. Here are seven not-so-nice things butterflies are into:

  • Getting drunk
  • Fighting
  • Eating meat
  • Eating poop
  • Drinking tears
  • Tricking ants
  • Raping pupae

Don’t get me wrong—I like butterflies. In fact, I like them more knowing that they have a dark side. They’re far more interesting, more weird, than any ode to pretty colors could convey.

Happy Learn About Butterflies Day!


Dino Martins. Flitting Emperors – and Forest Queens. SWARA Vol. 27 No. 2 / April–June 2004; pp. 52-55. No link available.

Dino Martins. ‘Mud-Puddle’ — or Be Damned. SWARA January—March 2006; pp. 66-68.

Queen Ants Make Distinctive Sounds That Are Mimicked by a Butterfly Social Parasite. Science: Vol. 323, Issue 5915, pp. 782-785. 2009.

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WATCH: Amazing Video Reveals Why Roaches Are So Hard to Squish

No door will stop them: American cockroaches can squeeze through a space just three millimeters high.
No door will stop them: American cockroaches can squeeze through a space just three millimeters high.
Photo Credit Tom Libby, Kaushik Jayaram and Pauline Jennings. Courtesy of PolyPEDAL Lab UC Berkeley


Have you ever stomped a roach, just to have it skitter away unscathed?* Or seen one disappear into an impossibly small crack?

Now scientists have figured out how they do that, and the results are terrifying.

The American cockroach (Periplaneta americana, aka “the big ones”) can squeeze through a crack the height of two stacked pennies in about a second—a fact newly discovered by two brave scientists who are probably still seeing roaches squeezing under the doors of their nightmares.

See for yourself:

Not only can roaches fit through tight spaces by flattening their flexible exoskeleton and splaying their legs to the side, the researchers found, they can keep running nearly as fast while squished, the team reports Monday in the Proceedings of the National Academy of Sciences. (In roach terms, top speed is 1.5 meters, or 50 body lengths, per second. Scaled up, that’s equivalent to a human running 200 miles per hour.)

Robert Full and Kaushik Jayaram at Berkeley built tiny tunnels and used a roach-squishing machine to test the animals’ limits. (No roaches were harmed—Full says “we only pushed them to 900 times their body weight, and they could still do that without being hurt.” In fact, they ran just as fast afterward.)

“We find them just as disgusting and revolting as everybody else,” Full says. But he also thinks they’re amazing, and is designing roachy robots that can squeeze and scuttle just like the real thing. The robots take inspiration from roaches’ jointed exoskeletons, with a design similar to folded origami.

A new compressible robot, nicknamed CRAM, is inspired by the flexible yet tough cockroach.
A new compressible robot, nicknamed CRAM, is inspired by the flexible yet tough cockroach.
Photograph by Tom Libby, Kaushik Jayaram and Pauline Jennings. Courtesy of PolyPEDAL Lab UC Berkeley

Full sees roaches and other arthropods—insects, spiders, and the like—as the next big thing in robots inspired by nature. Unlike other soft robots inspired by worms or octopuses, insect-bots with hard exoskeletons and muscles could run fast, jump, climb, and fly, while still remaining flexible.

“We know that cockroaches can go everywhere. They’re virtually indestructible,” Full says. For roaches, being able to scuttle quickly through small spaces has allowed them to spread into virtually every habitat imaginable and outrun their competition. Other insects probably have their own versions of these super-squishing superpowers, too, he says.

(For more on the positive side of roaches, learn why cockroaches made it onto our list of “All-Star Animal Dads.”)

The new roach study “transformed how I view a seemingly ‘hard’ animal,” says Daniel Goldman of Georgia Tech, who studies the physics of animal movement.  

“Their idea to create a “soft” robot out of deformable “hard” parts is great, and should transform how we think of creating all-terrain robots,” Goldman says.

*If you would never, ever, stomp on a roach, and are horrified at the suggestion, you’re a kind person and a sensitive soul. Keep watching the video though—it may surprise you.

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An Epidemic 14 Years Ago Shows How Zika Could Unfold in the US

An Aedes albopictus mosquito, which health authorities worry may begin to spread Zika.
An Aedes albopictus mosquito, which health authorities worry may begin to spread Zika.
Photograph by James Gathany, CDC.

If the Zika virus comes to the United States, we could face the threat of the same sort of virgin soil epidemic—an infection arriving in a population that has never been exposed to it before—that has caused more than 1 million known infections, and probably several million asymptomatic ones, in Central and South America. It’s nerve-wracking to wonder what that would be like: How many people would fall ill, how serious the effects would be in adults or in babies, and most important, how good a job we would do of protecting ourselves.

But, in fact, we can guess what it would be like. Because we have a good example, not that long ago, of a novel mosquito-borne threat that caused very serious illness arriving in the United States. And the data since its arrival shows that, despite catching on fairly quickly to what was happening, the U.S. didn’t do that good a job.

This possibility became more real Monday when the Pan American Health Organization released a statement that predicts Zika virus, the mosquito-borne disease that is exploding in South and Central America and seems likely to be causing an epidemic of birth defects especially in Brazil, will spread throughout the Americas. PAHO, which is a regional office of the World Health Organization, said:

There are two main reasons for the virus’s rapid spread (to 21 countries and territories): (1) the population of the Americas had not previously been exposed to Zika and therefore lacks immunity, and (2) Aedes mosquitoes—the main vector for Zika transmission—are present in all the region’s countries except Canada and continental Chile.

PAHO anticipates that Zika virus will continue to spread and will likely reach all countries and territories of the region where Aedes mosquitoes are found.

Those “countries and territories where Aedes mosquitoes are found” include a good portion of the United States, as these maps from the Centers for Disease Control and Prevention demonstrate:

CDC maps of the ranges of two mosquito species that could transmit Zika virus.
CDC maps of the ranges of two mosquito species that could transmit Zika virus.
Graphic from CDC.gov, original here.


The recent history is this: In the summer of 1999, the New York City health department put together reports that had come in from several doctors in the city and realized that an outbreak of encephalitis was moving through the area. Eight people who lived in one neighborhood were ill, four of them so seriously that they had to be put on respirators; five had what their doctors described as “profound muscle weakness.”

Within a month, 37 people had been identified with the perplexing syndrome, which seemed be caused by a virus, and four had died. At the same time, veterinarians at the Bronx Zoo discovered an unusual numbers of dead birds: exotics, like flamingos, and city birds, primarily crows. Their alertness provided the crucial piece for the CDC to realize that a novel disease had landed in the United States: West Nile virus, which was well-known in Europe, but had never been seen in this country before.

West Nile is transmitted by mosquitoes in a complex interplay with birds. It began moving with both birds and bugs down the East Coast and then across the Gulf Coast. As it went, the CDC realized that the neurologic illness that marked the disease’s first arrival had not been a one-time event, but its own looming epidemic within the larger one. “Neuroinvasive” West Nile, which in its worst manifestations caused not transient encephalitis but long-lasting floppy paralysis that resembled polio — and sometimes killed — bloomed in the summer of 2002 east of the Mississippi, and then moved west in the years afterward as the disease exhausted the pool of the vulnerable.

The CDC’s maps showing the emergence of “neuroinvasive” West Nile virus disease from 2001 to 2004; areas in black had the highest incidence.
Graphic by Maryn McKenna using maps by the CDC; originals available here.

So far, so normal, for a newly arrived disease. But here’s where the story gets complicated. By the beginning of this decade, West Nile had become endemic in the lower 48 states. It is not a mysterious new arrival; it is a known, life-altering threat. Its risk waxes and wanes with weather and insect populations, but it has one simple preventative: not allowing yourself to be bitten by a mosquito.

And yet: Here are the CDC’s most recent maps of neuroinvasive West Nile—showing that people are still falling to its most dire complication, 14 years after it was identified.

The CDC's maps for 2011-2014 showing the incidence of "neuroinvasive" West Nile virus disease; areas in black had the highest incidence.
The CDC’s maps for 2011-2014 showing the incidence of “neuroinvasive” West Nile virus disease; areas in black had the highest incidence.
Graphic by Maryn McKenna using maps by the CDC; originals available here.

The point here is not that people are careless or unthinking; in the early years of West Nile, two of the victims were the husband of the CDC’s then director, and the chief of its mosquito-borne diseases division, who would have been well aware of the risks. (Both recovered fully.) The point is that always behaving in a manner that protects you from a mosquito bite—conscientiously, persistently, faultlessly emptying pots and puddles, putting on long sleeves and repellent, choosing when not to go outdoors—is very difficult to maintain.

Zika is not West Nile. Among other things, Zika is spread by many fewer species of mosquitoes — one or possibly two, compared to 65 for West Nile. And West Nile’s non-human hosts, birds, live in closer proximity to more of us than Zika’s, which appear to be non-human primates. But though the rare, deadly complications of West Nile virus infection are different from those of Zika, they are just as serious and life-altering — and yet we failed to protect ourselves from them. As Zika spreads, we can hope that is a lesson we learn in time.

Previous posts in this series:

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Zika Virus: A New Threat and a New Kind of Pandemic

An Aedes aegypti mosquito, the chief vector of Zika virus.
An Aedes aegypti mosquito, the chief vector of Zika virus.

The leader of infectious disease research in the U.S. government says that the pandemic of Zika virus spreading across the global south, which may be causing an epidemic of birth defects in South America, heralds a new kind of infectious disease threat. It is exploding at the same time and in the same areas as other diseases carried by the same vector, mosquitoes—and thus demonstrates that it is no longer enough to be prepared to counter one disease at a time.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, writes in a study released Wednesday in the New England Journal of Medicine with Dr. David Morens of NIAID that Zika arrives in the Americas on the heels of three other mosquito-borne diseases: West Nile virus, in the United States since 1999 and still causing cases; chikungunya, which has invaded the Caribbean and Central America; and dengue, which moved north from the tropics to become re-established in Florida.

“Zika virus forces us to confront a potential new disease-emergence phenomenon: pandemic expansion of multiple, heretofore relatively unimportant arboviruses previously restricted to remote ecologic niches,” they write. “To respond, we urgently need research on these viruses and the ecologic, entomologic, and host determinants of viral maintenance and emergence. Also needed are better public health strategies to control arboviral spread.”

As I reported a month ago, Zika—which is often a mild disease of fever, aches and rash—has spiked extraordinary alarm in Brazil because it is overlaid with, and may be causing, an epidemic of babies being born with unusually small brains and heads. The microcephaly, as it is called, has not been proven to be caused by Zika, but people are so alarmed that, as one commenter here wrote, “People here are very worried about Zika virus, especially pregnant women and the ones trying to get pregnant… In the timespan of two weeks my city has gone from ‘never heard of this virus’ to thousands of infecteds, inclunding myself, my husband, and several relatives and friends of mine.”

At that point, Zika had spread from the shoulder of South America up through Central America and into Mexico. Since then, it has also been found in Puerto Rico, in a person who had not traveled outside the country—putting it on U.S. soil though not in the continental United States—and on Monday, in the vicinity of Houston, though that person was probably infected while traveling.

Zika, dengue and chikungunya are spread by the same mosquito species, A. aegypti, which has adapted to live near humans: It flourishes in small pools and containers of water, like a flower pot or the puddle in a tire. There are limited tests for the diseases—none for Zika, and sparsely distributed ones for the other two —and no treatments for them other than supportive care. Their initial symptoms are similar, but because they have different serious complications—birth defects for Zika, hemorrhagic fever for dengue, reactive arthritis for chikungunya—it is possible to make mistakes in the early stages that can make the late consequences worse.

The researchers argue that all of this adds up to a new responsibility to both prevent diseases, and also confront that prevention is a broader task than has previously been understood. In the case of these mosquito-borne diseases, a “one bug one drug” approach is inadequate, they say. What is needed: broad-spectrum drugs that can address whole classes of viruses, and vaccine “platforms” that can be adjusted as needed to prevent infection with whatever virus arrives on the scene. But more broadly, these diseases provide a lesson, of how rapidly and lethally emerging threats—possibly, multiple threats— will take us by surprise if we do not prepare.

“In our human-dominated world, urban crowding, constant international travel, and other human behaviors combined with human-caused microperturbations in ecologic balance can cause innumerable slumbering infectious agents to emerge unexpectedly,” they write. “We clearly need to up our game with broad and integrated research that expands understanding of the complex ecosystems in which agents of future pandemics are aggressively evolving.”


Previously on Phenomena:

Dec. 2, 2015: Mosquitoes Bring Disease, Maybe Birth Defects, to US Border.





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What Do Snails Think About When Having Sex?

It starts with a light, soft touch, one tentacle gently reaching out, hesitant, hopeful, hanging lightly in the air. There’s a pause. Skin touches skin. One softly strokes the other and slides closer, and then, carefully, they wrap themselves together, stroking, probing, entwining. They glisten as they move, and because they are snails, everything happens very slowly. The rubbing, the rapture, the intensity of it all—snail sex is extraordinarily lovely to look at. (If you aren’t at your office desk or on a train where people can see your screen, I’ve got one about a garden snail named Chip who’s trying to lose his virginity, or take a quick peek—30 seconds will do—of this coupling in a garden.)

Lovely but So Dangerous

Garden snails make love in the open—on garden patios, in clearings on the forest floor—and they do it luxuriantly for one, two, three hours at a time, under the sky, where they can be seen by jays, orioles, frogs, snakes, shrews, mice, beetles, and other animals that might want to eat them. Snails can’t make quick getaways, so exposing themselves like this is dangerous, crazily dangerous. What’s going on? What’s making them so impervious, so deeply preoccupied with each other? Here’s one answer: Snail sex is very complicated. Snails have a lot to think about when they make love—because they’re hermaphrodites.

Unlike you, garden snails can produce sperm like males and carry eggs like females at the same time.

Drawing of a proud snail, with its hands on its shell hips
Drawing by Robert Krulwich
Drawing by Robert Krulwich

Which is both an advantage and a problem. Professor David George Haskell, a Tennessee biologist, once squatted down on a patch of forest floor and watched what you just saw in that video—a snail couple going at it—except with a magnifying glass and only a few feet from the action. What he noticed was their mood. Hot as it was, he writes in his book The Forest Unseen, “Their extended courtship and copulation is choreographed like cautious diplomacy.” Snails don’t pounce, they circle. They “slowly edge into position, always ready to pull back or realign.” Their sex is tense, charged, on, off, then on again, “a prenuptial conference over the terms of the union.” What are they negotiating about?

In most animals, snails included, sperm is plentiful, cheap to produce, and fun to unload. So one presumes that both copulating snails are eager to get that part done.

A drawing of two snails, both looking at each other with thought bubble exclamation points above their heads
Drawing by Robert Krulwich
Drawing by Robert Krulwich

Eggs, on the other hand, are limited and hard to produce—and therefore precious. You don’t let just anybody fertilize your egg sack. So, in Haskell’s imagination, if one of these snails picks up “a whiff of disease” on the other, it may be happy to poke but is not at all interested in being poked. No one wants its precious eggs fertilized by a sick dad, so the receiving snail might lock its partner out of its opening while also trying to penetrate it. This could produce feelings of frustration, confusion, and even unfairness in the other.

A drawing of two snails looking at each other, one with an exclamation mark thought bubble and one with an X through an exclamation mark thought bubble
Drawing by Robert Krulwich
Drawing by Robert Krulwich

“In hermaphrodites,” writes Haskell, “mating becomes fraught, with each individual being cautious about receiving sperm while simultaneously trying to inseminate its partner.” Sexually speaking, two snails with four minds—a foursome in a twosome—makes for complex fornication. That’s why snails are always on tiptoe, Haskell thought as he watched them on the forest floor: They have so much to figure out.

Picture of a brown snail peering its head around to the side
Photograph by © Tetra Images / Alamy
Photograph by © Tetra Images / Alamy

Hermaphrodite Abundance

So why be a hermaphrodite? Are there a lot of them? Well, here’s a surprise: They’re everywhere.

Eighty percent of the plant kingdom produces both seeds (pollen) and eggs (ovules) and can give or receive, making them hermaphroditic. They’ve learned that when the weather gets wet or cold, bees can’t be depended upon to buzz by and pollinate, so they have a we-can-do-this-ourselves backup plan.

Animals, generally speaking, are sexual, divided into male and female. But, writes Stanford biology professor Joan Roughgarden in her book The Genial Gene, if you subtract insects, which make up more than 75 percent of the animal kingdom and are not hermaphrodites, we are left, she calculates, “ … with a figure of 1/3 hermaphrodite species among all animal species.” That’s a hunk of hermaphrodites.

So Who’s a Hermaphrodite?

They’re not animals we pay much attention to (flukes, flatworms, killifish, parrot fish, moray eels, barnacles, slugs, earthworms, and tapeworms, among many others), but they are switch-hitters: They can either give or receive or switch sides during their lifetime. “All in all,” writes Roughgarden, “across all the plants and animals combined, the number of species that are hermaphroditic is more-or-less tied with the number who has separate males and females, and neither arrangement of sexual packaging can be viewed as the ‘norm.’”

Anyone who thinks that male/female is nature’s preference isn’t looking at nature, says Roughgarden. And she goes further.

Adam and Eve or AdamEve?

She wonders, Which came first, the hermaphrodite or the male/female? We have lived so long with the Adam and Eve story—Adam first, Adam alone, Adam seeking a mate, God providing Eve—that the question seems almost silly: Of course complex animals started with males and females.

Painting of Adam and Eve in the Garden of Eden, Eve is offering Adam an apple
Adam and Eve, 1537 (panel), Cranach, Lucas, the Elder (1472-1553) / Kunsthistorisches Museum, Vienna, Austria / Bridgeman Images
Adam and Eve, 1537 (panel), Cranach, Lucas, the Elder (1472-1553) / Kunsthistorisches Museum, Vienna, Austria / Bridgeman Images

But Roughgarden wonders if animals started as hermaphrodites …

Composite of Adam and Eve painting, creating one person
Composite image of Adam and Eve created by Becky Harlan from original paintings by Lucas Cranach © [Royal Museums of Fine Arts of Belgium, Brussels / photo : Guy Cussac, Brussels]
Composite image of Adam and Eve created by Becky Harlan from original paintings by Lucas Cranach © [Royal Museums of Fine Arts of Belgium, Brussels / photo : Guy Cussac, Brussels]

… and then “hermaphrodite bodies disarticulate[d] into separate male and female bodies?” How would that have happened? Roughgarden cites a paper she did with her colleague Priya Iyer.

They propose that maybe the earliest animals started out as both sperm and egg carriers, and a subgroup got especially good at inserting their penises into enclosures, aiming, and directing the sperm to its target (the authors call it “home delivery”). They did this so effectively that they needed fewer and fewer eggs and essentially became sperm sharpshooters or, as we call them now, “males.”

That development gave others a chance to give up sperm altogether to concentrate on chambering their eggs in nurturing nooks, thereby becoming “females,” and so more and more animals found it advantageous to be gendered.

Ayer and Roughgarden aren’t sure this happened. They say that, on available evidence, the story can go “in either direction.”

The alternate view is almost the story you know. It’s Adam and Eve, with a twist: In the beginning, early animals were gendered—except when it was inconvenient.

If, for example, you imagine a group of, well, let’s make them snails …

Drawing of a group of snails standing in front of a volcano erupting
Drawing by Robert Krulwich
Drawing by Robert Krulwich

… and something awful happens—there’s a terrible disease, an ice age, a new ferocious predator, or maybe a volcanic eruption…..

Drawing of a snail all alone after the fallout of a volcanic eruption, standing in front of a volcano puffing smoke
Drawing by Robert Krulwich
Drawing by Robert Krulwich

… so that we’re left looking at a lone individual, all by itself, looking around for a reproductive opportunity, crawling across the landscape, hoping to bump into somebody, anybody, to reproduce with, and after a long, long, anxious period, it finally sees what it’s been looking for. It crawls closer, closer, the excitement building.

Drawing of a snail in a vast and sunny landscape seeing another tiny snail in the distance
Drawing by Robert Krulwich
Drawing by Robert Krulwich

But as it gets within wooing range, it suddenly sees that—oh, no—it’s the same gender!

A drawing of two snails with moustaches
Drawing by Robert Krulwich
Drawing by Robert Krulwich

No possibility of babymaking here. And this happens half of the time. (Statistically, that’s the likelihood.) Now instead of being your friend, male/femaleness is your enemy. What wouldn’t you give for a hermaphrodite, a he/she snail that could, in a pinch, be whatever sex you need it to be. With a hermaphrodite, you can (again statistically) always make a baby. What a relief. So maybe that’s what happened. Gender difference disappears when gender no longer helps produce more babies (and when you don’t have to stick around and be a parent).

Which is the true story? We don’t know. Maybe the only story is that nature is flexible. When gender is useful, you get genders. When not, you don’t. What we forget, being humans, is that there are so many ways to flirt, to combine, to make babies—and the world is full of wildly different ways to woo. Tony Hoagland knows this. He’s not a scientist but a poet who lives in New Mexico, and in his poem entitled “Romantic Moment,” he imagines a boy on a date who sits next to his girl imagining … How shall I put this? … how the Other Guys do it.

Romantic Moment by Tony Hoagland

After the nature documentary we walk down,
into the plaza of art galleries and high end clothing stores

where the mock orange is fragrant in the summer night
and the smooth adobe walls glow fleshlike in the dark.

It is just our second date, and we sit down on a rock,
holding hands, not looking at each other,

and if I were a bull penguin right now I would lean over
and vomit softly into the mouth of my beloved

and if I were a peacock I’d flex my gluteal muscles to
erect and spread the quills of my cinemax tail.

If she were a female walkingstick bug she might
insert her hypodermic proboscis delicately into my neck

and inject me with a rich hormonal sedative
before attaching her egg sac to my thoracic undercarriage,

and if I were a young chimpanzee I would break off a nearby tree limb
and smash all the windows in the plaza jewelry stores.

And if she was a Brazilian leopard frog she would wrap her impressive
tongue three times around my right thigh and

pummel me lightly against the surface of our pond
and I would know her feelings were sincere.

Instead we sit awhile in silence, until
she remarks that in the relative context of tortoises and iguanas,

human males seem to be actually rather expressive.
And I say that female crocodiles really don’t receive

enough credit for their gentleness.
Then she suggests that it is time for us to go

to get some ice cream cones and eat them.

Thanks to the poet Thomas Dooley for suggesting Tony Hoagland’s poem, and to Mr. Hoagland for giving us permission to print it here in full. Reading “Romantic Moment” I giggled a little to think of eating ice cream on a sugar cone as a homo sapien mating ritual—but thinking back, I think he’s onto something. The poem can be found in Tony Hoagland’s collection Hard Rain.

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Raindrops Keep Falling on My Head: A Mosquito’s Lament

This, in case you were wondering, is a mosquito.

Picture of a drawing of a mosquito
Drawing by Robert Krulwich
Drawing by Robert Krulwich

This is a raindrop.

Picture of a drawing of a blue raindrop
Drawing by Robert Krulwich
Drawing by Robert Krulwich

And here’s a puzzle. Raindrops aren’t mosquito friendly. If you’re a mosquito darting about on a rainy day, those drops zinging down at you can be, first of all, as big as you are, and, more dangerously, they’re denser. Water is heavy, so a single raindrop might have 50 times your mass, which means that if one hits you smack where it hurts (between your wings) …

Picture of a mosquito being hit by a drop of water
Photograph by Tim Nowack
Photograph by Tim Nowack

… you should flatten like a pancake. A study says a mosquito being hit by a raindrop is roughly the equivalent of a human being whacked by a school bus, the typical bus being about 50 times the mass of a person. And worse, when it’s raining hard, each mosquito should expect to get smacked, grazed, or shoved by a raindrop every 25 seconds. So rain should be dangerous to a mosquito. And yet (you probably haven’t looked, but trust me), when it’s raining those little pains in the neck are happily darting about in the air, getting banged—and they don’t seem to care. Raindrops, for some reason, don’t bother them.

Picture of a drawing of mosquitos flying through the air, dodging large blue raindrops
Drawing by Robert Krulwich
Drawing by Robert Krulwich

Why not? Why aren’t the mosquitoes getting smooshed?

How Mosquitoes Survive Raindrops

Well, in 2012 David Hu, a professor of mechanical engineering at Georgia Tech, became interested in this problem and decided to pelt some airborne laboratory mosquitoes with water droplets while filming them with a high-speed camera—4,000 to 6,000 frames a second instead of the usual 24. That way he could watch them in super slow motion and figure out what they’re doing when they’re out in the rain. He published his findings in a 2012 paper that I’m going to describe here in “executive summary” form. (His video, by the way, is waiting for you below, so you can see what he saw for yourself.)

What he found is that most of the time anopheles mosquitoes don’t play dodgeball with the raindrops. They do get hit but usually off center, on their long gangly legs, which splay out in six directions. The raindrop can set them rolling and pitching, but they recover quickly—within a hundredth of a second. But even in the worst case, where the mosquito gets slammed right between the wings—a dead-on collision, because the mosquito is so light compared to the heavy raindrop …

Picture of a drawing of a mosquito clinging onto a falling raindrop as it descends through the air
Drawing by Robert Krulwich
Drawing by Robert Krulwich

… it doesn’t offer much resistance, and the raindrop just barrels along with the mosquito suddenly on board as a passenger. Had the raindrop slammed into a bigger, slightly heavier animal, like a dragonfly, the raindrop would “feel” the collision and lose momentum. The raindrop might even break apart because of the impact, and force would transfer from the raindrop to the insect’s exoskeleton, rattling the animal to death.

But because our mosquito is oh-so-light, the raindrop moves on, unimpeded, and hardly any force is transferred. All that happens is that our mosquito is suddenly scooped up by the raindrop and finds itself hurtling toward the ground at a velocity of roughly nine meters per second, an acceleration which can’t be very comfortable, because it puts enormous pressure on the insect’s body, up to 300 gravities worth, says professor Hu.

Picture of a drawing of a mosquito inside a raindrop, falling through the air
Drawing by Robert Krulwich
Drawing by Robert Krulwich

300 Gs is a crazy amount of pressure. Eric Olsen, at his blog at Scientific American, says a jet pilot accelerating out of a loop-de-loop experiences “only about nine gravities (88/m/squared).” One imagines his cheeks all splayed, his face squishy, but hey, that’s a soft-skinned human. We’ve got mosquitoes here. Their heads are harder. They have exoskeletons. Sudden accelerations don’t hurt as much, but what mosquitoes should fear, what they do fear, are crash landings. The ground is a lot harder than a mosquito.

Picture of a drawing of a mosquito being squished by a large blue raindrop
Drawing by Robert Krulwich
Drawing by Robert Krulwich

So what a mosquito has to do is get off that raindrop as quickly as possible. And here comes the best part: In most direct hits, Hu and colleagues write, the insect is carried five to 20 body lengths downward, and then, rather gracefully—maybe helped by a dense layer of wax-coated, water-repellent hairs—gets up and “walks” to the side, then steps off into the air, almost like a schoolchild getting off of a bus (albeit a fast-moving bus hurtling toward its doom). It does this almost matter-of-factly, like it’s no big deal. A mosquito, Hu writes, “is always able to laterally separate itself from the drop and recover its flight.” Always. (Unless the raindrop hits them too close to the ground.) If you want to see this for yourself, take a look at Hu’s video.

Video by David Hu and Andrew Dickerson

The moral here, should we need one, is that if you’re a mosquito on a rainy day, the place to be is high off the ground, and if you’re a human who worries about mosquito safety (not a big group, I know), you can move on. They solved this one roughly 90 million years ago.

Picture of a drawing of a mosquito with its arm around a raindrop, as though they were friends
Drawing by Robert Krulwich
Drawing by Robert Krulwich
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How This Beetle Creates 500 Explosions Per Second In Its Bum

There are few defences more extreme than that of the bombardier beetles. These insects deliberately engineer explosive chemical reactions inside their own bodies, so they can spray burning, caustic liquid from their backsides. The liquid can reach up to 22 miles per hour, at temperatures of around 100 degrees Celsius. It’s painful to humans—watch Ross Piper take one to the face—and potentially lethal to smaller predators like ants.

The beetle mixes its chemical weapons within glands in its abdomen, each of which consist of two chambers. The reservoir chamber contains a solution of hydrogen peroxide and hydroquinones—that’s the fuel, inert on its own but always on the cusp of extreme violence. The adjacent reaction chamber contains enzymes like peroxidise and catalase—that’s the match.

The two chambers are separated by a valve that stops their contents from mixing. When the beetle is threatened, it opens the valve and contracts the muscular walls of the reservoir, emptying its contents into the reaction chamber. Match meets fuel. The enzymes react with the incoming chemicals in a violently explosive reaction that produces oxygen, water vapour, a lot of heat, and irritating chemicals called p-benzoquinones. This searing, noxious, steaming cocktail then forces its way out through an exit channel as a spray, which the beetle can aim using reflector plates on its abdomen.

The spray isn’t continuous. Instead, the beetle fires between 368 and 735 pulses every second. This extends the range of the chemicals and also potentially saves the beetle’s life. The reaction chamber may be reinforced with layers of sturdy materials like chitin and waxes, but still, lest we forget, it’s creating explosions inside its own body. By pulsing its spray, “it gives the chamber some time to cool down,” says Christine Ortiz from MIT. “A continuous spray would heat the beetle up a lot more.”

Her team, including graduate student Eric Arndt, have taken high-speed X-ray videos of living beetles doing their thing, to work out how they produce such a rapid train of pulses. “We cool the beetle down so it goes to sleep, and then fix it in [the path of] the X-ray beam,” she says. “As it warms up, it realises that it’s fixed and undergoes an explosion.”

The videos revealed that during a spray, the beetle squeezes its reservoir chamber with a constant pressure, and keeps its exit channel continuously open. Neither is responsible for the pulses. Those come from the valve that separates the two chambers.

When the valve opens, a droplet of reservoir chemicals enters the reaction chamber. Boom! The pressure created by the explosion forces a pulse out through the exit channel. It also pushes against a membrane that closes the valve, cutting off the supply of fuel. As the pressure in the reaction chamber drops, the membrane relaxes and the valve re-opens, letting another droplet through. Boom! This continues until the reservoir muscles finally relax and the beetle stops spraying.

RSC = reservoir chamber; RXC = reaction chamber; EC = exit channel; ICV = valve; EM = membrane.
RSC = reservoir chamber; RXC = reaction chamber; EC = exit channel; ICV = valve; EM = membrane.

The wonderful thing about this set-up is that the beetle pulses its spray passively. It doesn’t need to evolve any special muscles for rapidly opening and closing the valve, and it doesn’t waste energy on doing so. Instead, it staggers its explosions using their own force.

Ortiz thinks that these discoveries may be useful in designing armour that protects against explosions. That’s what her team does: they’ve studied the defences of oysters and fish, and even created prototype body armour based on the scales of an ancient fish called a bichir.

Reference: Arndt, Moore, Lee & Ortiz. 2015. Mechanistic origins of bombardier beetle (Brachinini) explosion-induced defensive spray pulsation. Science http://dx.doi.org/10.1126/science.1261166

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There’s More Than One Way to Decapitate An Ant

Tropical rainforests are home to lots of ants, which means that they’re home to lots of injured ants. Ant colonies frequently fight each other, leaving behind battlefields strewn with wounded workers.

That’s good news for phorid flies.

There are some 4,400 species of phorids. Although their lifestyles are diverse, a surprising number of them specialise in decapitating ants (or bees). The females lay their eggs inside their victims. When the maggots hatch, they move towards the ant’s head and eat its brain and other tissues. The brainless ant stumbles about in a fugue for weeks until its head eventually falls off. Sometimes, that’s because the fly has inflicted so much damage. In other cases, the maggot deliberately releases an enzyme that dissolves the connection between the ant’s head and body.

But in the rainforests of Brazil and Costa Rica, Brian Brown from the Natural History Museum of Los Angeles County has found a phorid that beheads ants in an entirely new way.

Brown is an authority on phorids and especially the ant-decapitating, bee-killing varieties. He has discovered around 500 species of them. In the field, he lures them in by crushing ants and other insects with forceps, and watching what arrives. Some phorids feed directly off the injured insects. Others lay their eggs inside. But one species, Dohrniphora longirostrata, did something different.

A female will land near a wounded ant and circle it. She darts in and out, touching the would-be victim and occasionally tugging on its legs and antennae. The goal, it seems, is to check just how incapacitated this incapacitated ant really is. If it’s too active, she retreats to find an easier mark.

Eventually, she climbs onto the ant and jams her mouthparts into its body. “The fly was nearly constantly in motion, probing from several angles,” writes Brown. “They made in-and-out, as well as rotational head movements.” In other words, she’s sawing.

A housefly’s mouthparts end in a spongy pad for soaking up fluids; in place of that, D.longirostrata has an extremely long proboscis, almost as long as its entire body. Under the microscope, the tip looks like a murderous Swiss army knife, with one fiendish spike and a couple of serrated steak knives. The fly jams this tip into an ant, cutting and severing. After some time, it yanks the head clean off.

Proboscis tip from Dohrniphora longirostrata. Credit: Brown et al, 2015.
Proboscis tip from Dohrniphora longirostrata. Credit: Brown et al, 2015.

The headhunting females typically dragged their bounty away, so Brown isn’t clear about what they actually do with the heads. They probably lay eggs inside. But the team sometimes saw the females slurping up the contents of the heads themselves, and upon dissection, these females never had mature eggs. Perhaps they need to gorge themselves on ant heads before their eggs can develop.

Brown has been crushing ants and watching flies for 30 years, in eight countries across South and Central America. In all that time, he has only ever seen this fly attacking wounded trap-jaw ants. It won’t target healthy workers that could easily overpower and kill them—the strike of a trap-jaw ant is among the fastest movements in the animal kingdom. It won’t attack injured crickets, grasshoppers, or termites either. It’s extremely picky, which means that even without the intervention of forceps-wielding biologists, there must be a lot of injured trap-jaws lying around the forest.

There are between 50 and 100 species of Dohrniphora flies and many co-exist in the same forests. Maybe they’re all picky specialists, each one decapitating its own preferred ant.

Reference: Brown, Kung & Porras. 2015. A new type of ant-decapitation in the Phoridae (Insecta: Diptera). Biodiversity Data Journal http://dx.doi.org/10.3897/BDJ.3.e4299

More: The world’s smallest fly is a phorid; at half a millimetre long, it could sit on a housefly’s eye, and probably decapitates really tiny ants.

Thanks to Alex Wild for the hat-tip.

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Why Does This Weird Insect Flash Warnings After An Attack?

Kate Umbers was hiking through Australia’s Snowy Mountains in the autumn of 2008, when she saw her first mountain katydid—a thumb-sized insect with the colour and texture of a dead leaf. “I recognised it from the guide books and picked it up excitedly,” she says. “It immediately vomited and flashed its bright colours.”

Emphasis on bright. The insect’s dull brown wing casings flew apart to reveal vivid bands of red, black, and electric blue. The inconspicuous leaf suddenly transformed into a garish Christmas bauble.

Many animals do something similar. When a threat gets close, they flash bright colours, show off distracting eyespots, strike aggressive poses, and spray off-putting chemicals. They hiss, rattle, puff, and arch. These spectacles are called deimatic displays and they are supposedly meant to distract or intimate predators. Bright colours, in particular, are often messages that scream: “I AM TOXIC; DO NOT EAT ME.” For some animals, these claims are bluffs. For the mountain katydid, they are genuine warnings—this insect is full of foul-tasting chemicals.

But Umbers noticed something unusual about its displays: the katydid only flashed its colours after an attack.

“I was struck by how easy it was to catch them and how little resistance they put up,” she says. “They waited until they had been grabbed before revealing any defences.”

This isn't even my final form. (Credit: Kate Umbers)
This isn’t even my final form. (Credit: Kate Umbers)

Together, with Johanna Mappes, whose work I’ve written about before, Umbers carefully tested 40 captive katydids. She found that they almost never used their displays when she tapped a pen near their heads, blew gently on them, or waved a book overhead to simulate a passing bird. They only flashed upon contact, when she poked them or tried to pick them up.

That made no sense. Animals are meant to use deimatic displays to avoid attacks. It’s no use screaming, “I’m dangerous,” when beaks are already grabbing you or teeth are already sinking into your flanks. “Not only does this seem like a pretty bad strategy, it is counter to current thinking on how deimatic displays work,” says Umbers. “There is no theory to allow for such an adaptation, and yet there it is.”

“It’s a neat study, which suggests that we might have misread some kinds of animal signals, and misunderstood the different uses that startle defences can have,” says Mike Speed from the University of Liverpool.

Mountain katydid in the field. Credit: Kate Umbers.
Mountain katydid in the field. Credit: Kate Umbers.

Umbers suspects that the insect might prioritise stealth over shock. It blends into its surroundings, and if it revealed its colours, it would instantly break its own camouflage. That would be worthwhile if the colours worked as intended. But if predators don’t encounter these katydids very often, they might not know what the warnings mean and attack anyway. And while many animals use deimatic displays as distractions, to give themselves time to escape, the katydid is terrible at fleeing. It lacks the powerful jumping legs of its relatives, and the females can’t even fly. It does, however, have a very tough shell.

So, the katydid’s strategy seems to be: hide for as long as possible, rely on a tough shell to withstand a first strike; and hope that a mouthful of foul chemicals will deter a second one. “The species is combining the best of both worlds by walking softly and carrying a big stick,” says Tom Sherratt from Carleton University

But why the colours? Umbers suggests that they might reinforce the off-putting nature of the insect’s foul taste. Sherratt agrees, and notes that other animals couple chemicals and signals in this way. Some caterpillars, for example, vomit noxious substances and make clicking noises, when touched.

Umbers is now trying to work out what actually eats the katydids—the most likely candidates are ravens and magpies—and how they react to different aspects of the insects’ defence.

“Startle displays seem quite common in nature but are very much understudied,” says Martin Stevens from the University of Exeter. “What makes them effective—unexpectedness, novelty, anomaly, conspicuous colours, and so on—isn’t clear. The current study is therefore a nice start in understanding this.”

Reference: Umbers & Mappes. 2014. Postattack deimatic display in the mountain katydid, Acripeza reticulata. Animal Behaviour http://dx.doi.org/10.1016/j.anbehav.2014.11.009

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The Guts That Scrape The Skies

Take a walk through the African savannah and you might stumble across huge mounds, made from baked earth. They tower up to 9 metres tall, and are decorated with spires, chimneys and buttresses. These structures are homes, nurseries, and farms, all in one. They are also guts. They’re part of one of the most fascinating digestive systems on the planet—a distributed organ that begins inside the bodies of tiny insects and expands into towers that scrape the skies.

They are the work of a termite, Macrotermes natalensis. Like most of its kin, it eats wood and other plant matter. There are vast amounts of energy locked within the chemical bonds of wood, a fact that we attest to whenever we burn logs to heat our homes. But breaking those bonds is a demanding task. Humans lack the enzymes for the job. Termites fare better, but despite their reputation, their wood-breaking toolbox is surprisingly sparse. Instead, they rely on help.

M.natalensis is a farmer, which grows a fungus in its nest. It feeds the fungus with scraps of wood that the workers collect, chew, and regurgitate. The fungus spreads through this slurry and digests it, breaking apart the complex carbohydrates (known as lignocelluloses) into smaller sugary building blocks. The termites then eat the resulting compost. In their guts, legions of bacteria and other microbes take over, breaking down the sugars even further. Without the fungus or the microbes, the termites would be unable to eat.

So, the termite’s digestive system isn’t just a tube that runs through its body. It’s also a web of fungal threads growing in the many chambers of its nest, and a mass of microbes nestled within its gut. It’s a community of creatures from at least three kingdoms of life, which live inside the insect and outside it. It fills the termite’s body, and extends into the architecture of its homes.

This digestive alliance is an ancient one. Termites evolved from cockroaches around 150 million years ago and ever since, they’ve relied on gut microbes to launch assaults on tough plants. Around 30 million years ago, the macrotermites, the group to which M.natalensis belongs, added a new partner to the mix by domesticating an aptly named fungus called Termitomyces. The contract that sealed this partnership was a binding one. There are now 330 or so species of macrotermites and all of them cultivate Termitomyces, and nothing else.

This alliance has been spectacularly successful. Macrotermites are found throughout Africa and South Asia, and they shape the fates of entire ecosystems. They are lords of decay, breaking down the corpses of fallen plants and returning their stored energy back into the world. By pooling their powers with other minute partners, these uber-roaches can build cathedrals that are as tall as trees, while converting actual trees into termite flesh.

Michael Poulsen from the University of Copenhagen and Haofu Hu from BGI-Shenzen in China have now deciphered the different roles of the partners by sequencing the genomes of M.natalensis, the fungus it grows, and the microbes in its gut.

Between them, they wield a vast toolbox of plant-breaking enzymes called glycoside hydrolases (GHs), which cut the chemical bonds that link simple sugars into complex ones. There are 128 families of GHs and the three partners have 118 between them—an almost complete set. Most of these tools come from the gut microbes, while the fungus and (to a much lesser extent) the termite plug important gaps in the collection.

The fungus and the microbes seem to divide their digestive labours between them. The fungus excels at splitting large carbohydrates like lignin and cellulose into their constituents, but it’s no good at breaking down those constituents. That fits with its biology. Termitomyces isn’t so much a wood-eater as a wood-breaker. It sunders lignin to get at other nutrients deeper within a plant, rather than as an act of digestion itself.

The termite gut microbes, however, have plenty of enzymes that target the simpler sugars that the fungus produces. In fact, Poulsen and Hu found that the microbes in M.natalensis have far more of these enzymes than those in other termites that haven’t domesticated fungi.

So, the fungus launches the opening assault while the gut microbes land the finishing blows. The termites themselves contribute very little to these digestive labours. Their role is to grow and nurture the other partners.

This is a significant achievement. Termitomyces mushrooms are edible to humans and prized as delicacies in certain parts of Africa, but we have never been able to cultivate them. Termites can. These tiny-brained creatures construct mounds with in-built ventilation and air-conditioning, providing cool, humid oases in the parched savannah, where fungi can thrive. By building and nurturing these gardens, and by harbouring the right microbes in their bodies, the termites effectively cultivate their own digestive systems.

Poulsen and Hu found another twist to this tale: the M.natalensis queen is an oddity. She has none of the gut microbes that are most common in her workers, and her impoverished communities can only digest the very simplest of sugars. This fits with her biology. A macrotermite queen is an egg-laying machine, her abdomen grossly distended into a huge, white, pulsating sac. She can’t move. Instead, she relies on her worker daughters (and the microbes in their guts) to feed her.

It wasn’t always like this. The queen founded the entire colony and seeded her daughters with their gut microbes in the first place. Her own communities must have shrivelled later, even as her body expanded. You can think of the entire colony—workers, microbes, fungus, mounds and all—as her digestive system. It’s a huge symbiotic network that provides her with food and ensures the continuance of her genes.

More on insect farmers: How Leafcutter Ants Evolved From Farmers Into Cows

Reference: Poulsen, Hu, Li, Chen, Xu, Otani, Nygaard, Nobre, Klaubauf, Schindler, Hauser, Pan, Yang, Sonnenberg, de Beer, Zhang, Wingfield, Grimmelikhuijzen, de Vries, Korb, Aanen, Wang, Boomsma & Zhang. 2014. Complementary symbiont contributions to plant decomposition in a fungus-farming termite. PNAS http://dx.doi.org/10.1073/pnas.1319718111

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Rhino Beetle Weapons Match Their Fighting Styles

When longswords first came into use in the 13th century, knights mainly used them to slash through an opponent’s chainmail. But once plate armour entered the battlefield, these slashes were useless. Now, sword-wielders had to thrust their weapons into gaps and weak points—a new kind of fighting that required a different kind of blade. Longswords evolved to be longer, narrower, and more pointed. The central groove (the fuller) that lightened and strengthened the old models was replaced by a ridge (the riser) that conferred rigidity. A cutting weapon became more of a stabbing one. Form followed function.

Erin McCullough from the University of Montana found a similar trend among smaller but no less impressively armed combatants—rhinoceros beetles. As their name suggests, the males of these large, powerful insects have elaborate horns on their heads. In many animals, females choose males on the size and shape of their ornate structures. But that’s not the case for the rhino beetles. Their horns are purely weapons. They’re for grabbing, throwing and shoving rival males off branches and tree trunks, in a bid to control access to females.

Hercules beetle. Credit Udo Schmidt.
Hercules beetle. Credit Udo Schmidt.

Each species of rhino beetle has its own distinctive headgear, and each fights in a different style.  The largest of them, the Hercules beetle (Dynastes hercules) has a huge horn curving down from its back and another curving up from its head. It looks like a disembodied pincer, and behaves like one too—males grab their opponents in a full-body hold, prise them off their perch, and toss them to the ground. (It can lift 850 times its own weight and, until recently, held the title of world’s strongest animal .)

The calliper beetle (Golofa porteri) has a much narrower horn with a serrated edge, which it uses to lift and shove its opponent—more of a fencer to the Hercules beetle’s wrestler. And the Japanese rhino beetle (Trypoxylus dichotomus), much beloved of cartoons and anime, has an upwardly curving horn that ends in a pitchfork. During fights, it tries to slide this tip under its opponent, to lift and twist it off its branch.

“Your Hercules Beetle style is no match for my Caliper Beetle Fist Technique.” Different fighting moves of the Japanese rhino beetle (top), Hercules beetle (middle) and caliper beetle (bottom).
"Your Hercules Beetle technique is no match for my Caliper Beetle form!" Different fighting styles of the Japanese rhino beetle (top), Hercules beetle (middle), and caliper beetle (bottom). Illustrations by David J. Tuss

McCullough has found that the shape and structure of these horns are beautifully adapted to each beetle’s individual fighting style. Each one resists the types of forces that its owners typically experience, but threatens to snap or buckle when used in a different way. As with the longswords, form and function are linked.

This study wouldn’t have been possible through direct experiments. You can’t just pack a rhino beetle off to a new dojo, train it in a different martial art, and see how it performs. But McCullough did something similar, using a technique called finite element analysis (FEA). It’s a digital crash-test. You scan an object to create a three-dimensional virtual model, and then subject that model to forces of your choice. Engineers use it to simulate collisions between vehicles and obstacles. Biologists have used it to simulate collisions between jaws and prey. And McCullough used it to simulate collisions between beetles. In her computer, she could watch what happens if one rhino beetle fought its rivals in the style of another.

And what happens is: the horns do badly. For example, if you apply twisting forces to a Japanese rhino beetle’s horn, it holds up well. The virtual models are coloured in cool blues and greens, indicating low levels of mechanical stress. But if you twist the horns of the other two beetles, they light up in fierce reds and whites. In real life, they’d probably snap. In all three cases, McCullough found that the horns were least likely to snap or bend, when used in the directions that the beetles actually use them.

Cross-sections of the horns of the three beetles. Credit: McCullough et al, 2014. PNAS.
Cross-sections of the horns of the three beetles. Credit: McCullough et al, 2014. PNAS.

Some studies have shown that horned mammals also fight in ways that suit their headgear. Curved-horn sheep ram each other, short-horned gazelles stab, and long-horned oryxes wrestle. But none of these studies checked if the horns actually work best in these conditions, and whether they’d suit other techniques  equally well. McCullough did that with her virtual crash-tests. “It’s intuitive but this is the first real direct evidence of that hypothesis,” she says. “It shows the possibility of using this new tool—finite element analysis—for understanding weapon diversity.”

She also correctly predicted the cross-sectional shapes of the three beetles’ horns, based on their fights. The Hercules beetle mostly uses its horn to grab and lift, so its ideal cross-section is an oval that’s vertically wide and horizontally narrow. The calliper beetle’s horn is used in more versatile ways and needs to resist forces in most directions—it should have a circular cross-section. And since the Japanese rhino beetle’s horn often twists, it would benefit from a U-shaped or a triangular cross-section resists bending and twisting. And that’s pretty much what the three horns are actually like. Based on function, you can predict form.

McCullough says that the results show how “male–male competition can drive the diversification of animal weapons”. But I wondered if the beetles could instead be fighting in a way that makes best use of their horns? A human fighter wouldn’t try to pummel someone with a dagger or to stab someone with a mace. Maybe function follows form?

“I get asked that a lot,” she says. She thinks that behaviour is probably more flexible than horn structure, so it’s more likely that the former changed to fit the latter than the other way round. But the only way to be sure is to test a wider range of beetles and to see how both their weapons and their combat techniques changed as the group diversified. Her group, led by Doug Emlen, is now working on that.

For more on the rhino beetles and other weapons, you may want to check out Doug Emlen’s upcoming book Animal Weapons: The Evolution of Battle.

Reference: McCullough, Tobalske & Emlen. 2014. Structural adaptations to diverse fighting styles in sexually selected weapons. PNAS http://dx.doi.org/10.1073/pnas.1409585111



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Newly Discovered Wasp Plugs Nest With Cork of Ant Corpses

Here’s a  great home security tip from nature: if you don’t want people breaking into your house, stuff your hallway with corpses. Ideally, use the corpses of dangerous and foul-smelling people.

For specific hints, you need to travel to the forests of China. There, Michael Staab from the University of Freiburg has discovered a new species of wasp that protects its young by stuffing the entrance to its nests with ant cadavers. The practice reminded him of European ossuaries—buildings like the amazing Sedlec Ossuary that are piled high and deep with human skeletons. In honour of these sites, Staab named the insect Deuteragenia ossarium. It’s the bone-house wasp.

Staab discovered the creature as part of a huge project to study the ecology of China’s forests. He was especially interested in spider-hunting wasps that nest in cavities, such as mud cells that they build themselves or tunnels bored by beetles. These insects are hard to spot. To study them, Staab’s team set up artificial nests, consisting of hollow canes strapped to a post.

Female wasps built their nests in 829 of these canes, and most followed a standard design. They drag a paralysed spider into the far end of the cane, lay an egg on it, and then seal it off with a plug of resin, plant matter, and soil. The wasp then returns with another spider and repeats the process, until the hollow cylinder is filled with a row of separated ‘brood cells’. When the young wasps hatch, they devour their spider meals, transform into adults, and then chew their way out through the plugs.

Staab saw this pattern again and again. But in 73 of the nests, he found a surprise: the final chamber was packed with up to 13 dead ants. You can see this clearly in the image on top. Each cell in the long cane contains the cocoon of a wasp grub which had long since eaten its spider. The ants are on the far left, like some gruesome corpse cork.

The wasp that emerged from these nests had never been seen before—a pitch-black, half-inch-long insect with a small golden beard. It was clearly part of the Deuteragenia group, but it’s the only one of the 50 known species that plugs its nests with ants.

“We do not know if it actively hunts for the ants or if the specimens are collected from the refuse piles of ant colonies,” says Staab. “However, since all ant specimens were in a very good condition and not seriously decayed, we think that the wasp does actively hunt living ants.”

He’s also certain that the antechamber protects the wasp’s young. Cavity-nesting wasps may be parasites that feed their young on spiders, but they have parasites of their own: flies and other wasps that lay eggs on their young. Staab found these ‘hyperparasites’ in 16 percent of the nests that he set up, but a mere 3 percent of the bone-house wasp’s nests.

He thinks the ants are responsible for this difference. Ants are covered in distinctive chemicals that help them to recognise each other and can persist on the shells of dead individuals for a long time. These chemicals could confuse parasites that are searching for wasp nests. They might also be active deterrents, since ants are powerful predators that viciously defend their colonies against intruders. Indeed, Staab found that the ant most commonly found in a bone-house wasp’s nest is a big aggressive species with a powerful sting.

Ants are such good predators that many animals use them to protect themselves. The caterpillars of blue butterflies turn ants into bodyguards and babysitters by mimicking their sounds and smells. The banded cat-eyed snake also lays eggs in the gardens of leaf-cutter ants. And one species of assassin bug covers itself with the bodies of the ants that it eats—a coat of many corpses that puts off spiders, and rivals the bone-house wasp’s ossuary in the grisly stakes.

Reference: Staab, Ohl, Zhu & Klein. 2014. A Unique Nest-Protection Strategy in a New Species of Spider Wasp. PLoS ONE 9(7): e101592. http://dx.doi.org/10.1371/journal.pone.0101592

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How A Microbe Became A Living Supplement For A Tiny Vampire

Bedbugs have been sucking our blood for millennia and after a brief retreat following World War II, they are back and more numerous than ever. Infestations are rising, hotels are worried, and people are very, very itchy. But the bedbug isn’t solely responsible for its success. It has an accomplice.

Mammal blood is an unusual meal. It’s loaded with proteins and fats, but bereft of some vital nutrients like B vitamins. If you’re going to make a living off vampirism, you need to somehow supplement your diet. Bedbugs do it with bacteria. Scientists have suspected as much since the 1920s when they discovered that bedbugs have a pair of organs called bacteriomes that are full of bacteria. But it wasn’t till 2010 that Takema Fukatsu from the National Institute of Advanced Industrial Science and Technology in Japan finally identified the species that lives in these organs.

It’s called Wolbachia. Fukatsu found it in the bacteriomes of every bedbug he examined, and showed that females pass it to their offspring when they are still embryos. Wolbachia provides the insect with the B vitamins that it misses in its diet; kill the bacterium, and the bedbug grows slowly and can’t reproduce.

Wolbachia is arguably one of the most successful bacteria on the planet, colonising two out of every three species of insect. It’s not surprising to find it in a bedbug, but its role as a living supplement is stranger. Biologists typically see Wolbachia as a parasite. Since it always passes from mother to offspring, it has no need for males and has evolved many strategies for getting rid of them, including killing them outright or converting them to females.

But in the bedbug, it does nothing of the kind. Instead, this selfish “master manipulator” has become an important ally. It’s more body part than puppet master. How did it evolve that way? Once again, Fukatsu’s team has the answer: it borrowed a package of genes from other bacteria.

Adult bedbug, by Takema Fukatsu.
Adult bedbug, by Takema Fukatsu.

The team, including Naruo Nikoh, Takahiro Hosokawa and Minoru Moriyama, sequenced the genomes of Wolbachia from several bedbugs in Japan and Australia. Inside, they found an unusual cluster of six genes that allow these microbes to make vitamins B7 (biotin) and B1 (thiamine).

These genes are vital. If the team killed off the Wolbachia strains with antibiotics, the bedbugs couldn’t grow normally or reproduce unless they were fed on blood that was fortified with B vitamins. And when the team specifically took biotin out of this supplemental cocktail, the insects suffered again. The bedbugs depend on biotin and, by extension, on the microbes that make it.

The biotin cluster isn’t a feature of Wolbachia in general; the team only found it in strains that infect bedbugs (and the closely related batbugs). But it also exists in many other bacteria that infect insects. This strongly suggests that this sextet of genes isn’t an invention, but a loan. The ancestor of the bedbug’s Wolbachia picked it up from another microbe that infected the same host. “These genes are rampantly moving across diverse bacterial lineages,” says Fukatsu.

This is evolution in sixth gear: fast and dramatic. Wolbachia picked up the right genes from another species, and its bedbug host suddenly gained the ability to supplement its diet. That event may well have sealed the partnership between the insect and the microbe.

The partnership must be a recent one. The genomes of bacteria that live inside insect cells—endosymbionts—always waste away with time, abandoning any genes that they once needed for a free-living existence. But the bedbug’s Wolbachia still has a relatively intact genome, which means that it hasn’t been an endosymbiont for very long.

What will happen to it as the millennia tick by? We can find clues by looking at other insects. Aphids have similar problems to bedbugs. They drink a fluid—plant sap—that lacks a number of important nutrients, and they rely on an endosymbiont called Buchnera to supplement their diet.  These two have been co-evolving since the dawn of the dinosaurs. If you chart the family tree of Buchnera strains, it looks almost identical to the family tree of aphids. And while killing Wolbachia harms a bedbug, killing Buchnera kills its aphid host too.

Plant sap lacks more nutrients than blood, so the symbionts of sap-suckers tend to be more indispensible than those of blood-feeders. Still, it’s conceivable that the bedbug’s Wolbachia could head down the same evolutionary path as the aphid’s Buchnera.

A bedbug, then, is a continuously changing concept. One evolutionary moment, it’s an insect. The next, it’s an insect with a bacterial partner. Perhaps in the future, the two will become so inextricably linked that it makes no sense to talk about them as parts of a whole—just as a whole. After all, there’s at least one insect with Wolbachia’s entire genome inside its own.

Reference: Nikoh, Hosokawa, Moriyama, Oshima, Hattori & Fukatsu. 2014. Evolutionary origin of insect–Wolbachia nutritional mutualism. http://dx.doi.org/pnas.org/cgi/doi/10.1073/pnas.1409284111


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The Silence of the Crickets, The Silence of the Crickets

In 2003, Marlene Zuk travelled to the Hawaiian island of Kauai and heard something very strange—nothing. A disquieting quiet. An absence of chirping. A silence of the crickets.

Zuk had been studying crickets in Kauai since 1991, back when the insects were both noisy and plentiful. But every time she went back, she heard fewer and fewer of them. In 2001, she heard a single calling male. By 2003, the silence was complete.

The crickets hadn’t disappeared. Zuk would go for nighttime walks and see multitudes of the insects in the light of her headlamp. If anything, there were more of them than before. They just weren’t calling out. When she dissected them, Zuk found out why.

Male crickets call with two structures on the backs of their wings—a vein with several evenly spaced teeth (the file) and a raised ridge (the scraper). When the cricket rubs these together, the effect is like running your nail along the teeth of a comb—you get a thrrrrrrrrrrrp sound. But on all the silent Kauai crickets, the file was growing at a weird angle and had all but disappeared. Their wings were flat.

This change hobbled their courtship songs, but likely saved their lives. In the 1990s, Zuk’s team discovered that the crickets were targeted by a parasitic fly, whose larvae burrow inside them and devour them alive. The flies finds the crickets by listening out for their songs and they’re so effective that, in the early 90s, they had parasitised a third of the males. In 2002, the cricket population had fallen dramatically, and Zuk thought that they were done for.

But the silent males escaped the attention of the fly. As they bred and spread, they carried the flatwing mutation with them. By 2003, the cricket population had rebounded. And in fewer than 20 generations, they had gone from almost all-singing to almost all-silent. The crickets have become a classic textbook example of rapid evolution.

Then, a few years later, the team found that exactly the same thing had happened on the neighbouring island of Oahu! In 2005, for the first time, they found four flatwing males on the island. By 2007, half the males were flatwings.

At first, they thought that the flatwing mutation arose once on Kauai before spreading to Oahu. That made sense: with just 70 miles between the islands, it seemed possible—likely, even—that boats or strong winds carried the flatwing males across to Oahu. When they arrived, they bred with the locals, and their beneficial mutation spread.

But that’s not what happened.

In a new study, Sonia Pascoal from the University of St Andrews has found that this case of evolutionary déjà entendu is actually an example of convergence. The two populations of crickets, threatened by the same eavesdropping parasite, independently evolved similar flattened wings, at pretty much the same time, in just a handful of years.

Normal wings versus flatwings. Credit: Nathan Bailey.
Normal wings versus flatwings. Credit: Nathan Bailey.

Pascoal’s first clue was that the wings of the silent Kauai crickets look different on those of the silent Oahu ones. You can even tell the two groups apart by eye.

Genetic tests revealed even bigger differences. On both islands, the flatwings are caused by a mutation on a single gene, somewhere on the X chromosome. But both mutations arose independently!

Pascoal’s team looked for genetic markers that flank the flatwing mutation and are inherited together with it. They found more than 7,000 of these, but only 22 were common to both populations. This strongly suggests that the two flatwing mutations arose independently of one another. They seem to have arisen on different versions of the X chromosome. They may even have arisen on different genes or on different parts of the same gene.

“It was quite a surprise!” says Nathan Bailey who led the new study (which Zuk is also part of).  “There is solid evidence that evolution can act in the proverbial blink of an eye, but the bulk of this comes from laboratory studies where it is much easier to control conditions. What’s unique about these crickets is the nearly simultaneous appearance of the mutations on two islands.”

The team still have to identify the mutations (or gene) responsible for the flat wings. They also want to know why they arose and what they do. Did the two populations have different starting conditions, that influenced the mutations they eventually gained? Is there a hotspot in the cricket genome where mutations that shape the wings can easily emerge? And do the mutations lead to flat wings in the same way?

The answers will come in time. Just as Zuk’s discovery of the silent crickets gave us a great example of rapid evolution to study, this new discovery provides an excellent opportunity to look at convergent evolution in its earliest stages.

“Many studies that examine convergent evolution are faced with the difficulty that the appearance of mutations that cause similar adaptations in different populations may have occurred very long ago,” says Bailey. “That makes it difficult to tell whether traits with similar functions were derived independently, or whether they share a common ancestry.” I wrote about one such example last week: scientists only recently realised that large, flightless birds like ostriches, emus and rheas evolved their grounded, giant bodies independently of one another.

But on Kauai and Oahu, Zuk and her colleagues have found an example of convergent evolution, happening in real-time. “It’s an extraordinary opportunity,” says Bailey.

Reference: Pascoal, Cezard, Eik-Nes, Gharbi, Majewska, Payne, Ritchie, Zuk & Bailey. 2014. Rapid Convergent Evolution in Wild Crickets. Current Biology. http://dx.doi.org/10.1016/j.cub.2014.04.053