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What Halloween Decorators Know About Spiders (Oddly, a Lot!)

Here was my Halloween plan: not original, I know, but classic, effective, and cheap.

My front door, I decided, would become a lush, over-the-top spiderweb, a luxuriant Donald Trumpian display of muchness, which means … I would need two, maybe three, stretch-to-fit spiderwebs.

I don’t know the dimensions of my door (does anyone?), and I didn’t want to think about this for more than, oh, two minutes, so after a quick (and useless) trip to the Halloween section of my local drugstore, I jumped to the other web, the worldwide one, where I found (yes!) a nonflammable “Stretchable Spider Web” 12-pack for $10.99, with (yes!) a complimentary half-inch plastic spider, which (yes!) works out to about 90 cents per web (not including thumbtacks or tape). Good price. But—when I opened it—bad web.

It’s one of these …

A spider web decoration spreads across the ceiling
Photograph by VirtualWolf, Flickr

I was hoping for a classic, top-of-the-line spiderweb with a cool hole in the middle and surrounded by radiating spirals of silk, like the ones you see on trees, bushes, and the cover of Charlotte’s Web, capable of having “Terrific!” or “Some pig!” written on them, what arachnologists call an orb web, like this …

Picture of an orb spider web in Dover, Delaware against a black background in an outdoor setting
Photograph by George Grall, National Geographic Creative

But Halloween orb webs are pricey. Target wants $14 for just one. (It comes with lights, but still …)

Instead, what I got in my nonflammable 12-pack was a lesser design. They call them tangle webs or, worse, sheet webs, like the ugly one here …

a sheet spider web spreads across a bush
Photograph by Paul R. Sterry, Alamy

These messy, disorganized clumps are the work, I imagined, of low-rent “beginner” spiders who haven’t yet learned how to do it beautifully. So I was a little bummed. I even went to a couple of spider sites to see what evolutionary losers inspired my 12-pack.

But what I found shocked me.

Orb webs are not considered spider masterpieces. Not by spider scholars. Don’t be fooled by how beautiful, symmetrical, and lyrical they are. Spiders have moved on.

“More advanced spiders,” says Paul Selden, a spider paleontologist at the University of Kansas in Lawrence, “have gotten rid of [orb webs] and developed something else.”

It’s true. I found a bunch of papers that say orb webs are very ancient creations. These days, they’re considered “primitive.”

Turns out that webs like Charlotte’s require a fairly big spider (many spider species are small); worse, these webs need their spiders to stay close, which means they can be spotted and eaten by predators; still worse, they’re not that easy to navigate. Some of them have really sticky parts that can trap their spider. Which is why more highly evolved spiders have stopped making them.

So what are more evolved spiders making instead?

Unbelievably enough, they’ve moved up (up?) to sheet webs and cobwebs—the hideous things I found in my 12-pack!

An extensive survey of newer species found that the spiders that used to make orb webs have stopped, switched, and evolved into sheet and cobweb makers. Two of the fastest growing spider types, says biologist Jon Coddington, “are linyphiids (sheet webs) with 4,378 extant species, and theridiids (cobwebs) with 2,310 extant species.”

A cobweb on a lightbulb
Photograph by sogni_hal, Flickr

That means the little web you keep sweeping away in the corner of your garage or up in the attic, that sad little thingy that looks like it should stay in the corner, is—who would have guessed?–a considerably improved bit of spider design. Cobwebs, says science writer Sue Hubbell, are “more elaborately engineered, denser, safer for the spider and more efficient for trapping prey.”

So what if they’re ugly? Spiders aren’t trying to please me. They’re trying to get dinner. Ugly webs, apparently, are just better for spiders than beautiful ones, and if you doubt that, all you have to do is look at an evolutionary tree of spider webs.

Just tap on my “cover” tree (it’s a hyperlink that will take you to the tree I want you to see) and look for the orb webs. They’re not at the top … not at all …

Drawing by Robert Krulwich
Drawing by Robert Krulwich

Which means I’m reconsidering the biological sophistication of the Halloween decoration industry. I don’t know how many arachnologists my local drugstore has on staff (zero?), but what they’re selling this year is biologically, and evolutionarily, top of the line. What’s more, you can get a dozen of these gems for the low, low price of 90 cents.

This is a great country we live in.

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Social Spiders Pick The Best Careers For Their Personalities

I was a terrible scientist; I’m much better at being a writer. I lack the creative spark for designing clever experiments, but I can fashion a decent metaphor. My intellectual skittishness stops me from narrowing in on a single field, but it’s a boon when it comes to dealing with a broad spectrum of topics. It took me two unsuccessful years as a PhD student to work this out, and to find a job that’s better suited to my skills and temperament. Because of that, I envy the spider Anelosimus studiosus. It naturally falls into the right career.

While most spiders hunt alone, there are a few hundred species of social spiders that live in colonies. A.studiosus is one of them. Up to 50 individuals gather together to spin large collective webs, which ensnare larger prey than each spider could trap on its own.

All the colony members look the same, but they don’t all behave in the same way. The females can be aggressive or docile. It’s surprisingly easy to suss out their personalities: just put two of them in a small box overnight and check on them the next morning. If they’re both docile, they will have built a joint web in one corner of the box. If one of them is aggressive, the pair will be at opposite corners (you can then pair each individual with a known docile spider to confirm its personality).

Colin Wright from the University of Pittsburgh has now found that these personality types do different jobs within the web, creating a natural division of labour. They’re a little like ants and termites, where small workers clean and forage, and big soldiers guard and defend. But unlike these social insects, the social spiders don’t have distinctive castes with different physiques. Instead, their roles are defined by their personalities.

Social spider web. Joe Lapp
Social spider web. Joe Lapp

When Wright’s team, led by Jonathan Pruitt, first started studying A.studiosus, they couldn’t work out what the docile spiders did. They didn’t seem to repair webs, repel invaders, or catch prey. “The prevailing theory was that they were probably social parasites, a sort of selfish variant that freeloaded on the success of aggressive spiders,” says Wright.

But when the researchers checked the fates of colonies in the wild, they found that those with a mix of docile and aggressive members were more likely to survive than those with just a single type. The docile members were clearly doing something important.

It turns out that they act as the colony’s babysitters. They spend most of their time standing watch over the eggs, sitting amid clusters of spiderlings, or directly feeding the youngsters by regurgitating food—just like a mother bird might. Meanwhile, the aggressive spiders generally avoid these tasks; instead, they spend most of their time building the communal web, catching prey, and defending their colonies. (Although aggressive spiders repel docile ones in a simple container, the two types happily share webs—their different tasks mean that they rarely interact.)

The team also found that across the spiders show a perfect match between aptitude and career. That is, they tend to do the jobs that they’re best at.

Compared to the docile spiders, the aggressive ones are better at repelling a rival species of spider from their webs, at building webs that restrained crickets for longer, and at successfully subduing crickets that landed in their webs. This is probably because the docile females rarely respond to intruders—even prey—and when they do respond, they do so slowly.

By contrast, the docile spiders were better at looking after the colony’s young. When challenged with large broods, they raised twice as many to the point when the youngsters no longer needed care. That’s probably because  they’re less likely to fight with their youngsters over food. They’re also less likely to eat the spiderlings—one of the more important signs of a good parent.

“Rarely are results of a study so clear and interpretable,” says Wright. “We thank our spiders for being such a pleasure to work with.”

The results clearly show that something as subtle and hidden as a spider’s personality can help to organise its society. “Most people are more concerned with the physical characteristics of a species, and the idea that spiders have personality sounds somewhat like the topic of a children’s book,” he says. “But spider personalities are very real, and if you overlook them, at least in this species, you miss so much of the story!

For now, it’s not clear why the spiders naturally fall into their respective careers, or even what drives their different personalities in the first place. They seem to be largely heritable, but no one knows whether the spiders also learn to behave in a certain way, or if they can switch their personalities in certain situations.

And there’s another crucial piece of missing information, says Trine Bilde From Aarhus University, who has also studied social spiders: it’s not clear if the two types of spider are actually helping each other. “We don’t know whether docile females are fostering offspring of aggressive females, or if the aggressive females are sharing their catch with docile females,” she says.

The team are now trying to answer these questions. In the meantime, Wright suggests that biologists should pay more attention to personality types, when trying to understanding how animal societies work. For example, division of labour, of the kind that Wright studied, has been linked to the evolutionary origins of physically distinct castes in ants, bees and termites. But while physical castes only exist in a narrow range of animal groups, “individual differences in personality have been detected in almost every animal system imaginable,” says Wright.

“We feel that, in just about every instance, one could simply replace the word caste with personality,” says Wright. As with the spiders, this approach could help scientists to discover hidden variations in the behaviour of animals that otherwise look exactly the same—variations that could shape the structure of their societies in important ways.

Reference:  Wright, Holbrook & Pruitt. 2014. Animal personality aligns task specialization and task proficiency in a spider society. PNAS http://dx.doi.org/10.1073/pnas.1400850111

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Spider Hides From Spider Among Spider-Eating Ants

Most spiders only eject silk from glands in their rear ends but Scytodes—the spitting spider—is an exception. It can also shoot silk from its mouthpart. It does so with great force, and it impregnates these strands with venom to create a sticky gum that both poisons and traps its victims. It’s the closest natural equivalent to Spider-Man’s web-shooters.

If the prospect of a spider with a long-range weapon freaks you out, you are not alone. Even other spiders are wary of Scytodes.

In the Philippines, the spitting spider will readily attack jumping spiders and its web is often littered with arachnid carcasses. Ximena Nelson and Robert Jackson from the University of Canterbury have shown that it often targets a black-and-lemon species called Phintella piatensis. Scytodes will build its nest directly over a Phintella nest and ensnare the jumping spider as it enters and leaves its home. Sometimes, it even taps on the nest with its legs, perhaps to check if anyone’s home.

But Phintella is not entirely defenceless. Nelson and Jackson also found that it protects itself by nesting in the company of the weaver ant Oecophylla smaragdina.

When the duo placed leaves with Phintella nests in a chamber, and wafted in the smell of weaver ants, they found that Scytodes avoided building its own web overhead. And Phintella, in turn, was more likely to build nests on leaves where the ants could be seen or smelled.

Weaver ant kills Phintella. Credit: Robert Jackson
Weaver ant kills Phintella. Credit: Robert Jackson

The reason is simple: the ants are voracious predators and spiders are on their menu. They’re so aggressive that farmers often deliberately use them to protect mango crops from pests. Even Scytodes’ trademark weapon is of little use: its spit will immobilise a couple of weaver ants, but it can’t pin down an entire group. When Nelson and Jackson housed a Scytodes with weaver ants, it was almost always killed.

Phintella, however, isn’t bothered by the weavers. It fashions a silken cocoon like most jumping spiders do, but it uses an especially tough and dense weave that the ants cannot tear open. It also builds doors! It has hinged silken flaps at either end of its nest which seal it away when it’s inside the nest, and which the ants rarely try to open. The ants do sometimes capture Phintella, as the image above shows, but this is relatively rare.

So, its ant-proof home allows Phintella to surreptitiously recruit the weavers as protectors, without succumbing to them itself. It’s like a person who seeks safety by walking into the most dangerous part of town in a Kevlar suit.

There are many cases where ants act as bodyguards for other species, including aphids, acacia trees, and some butterflies, in exchange for food and nutrients. But the relationship between Phintella and the weavers isn’t a mutualism, where both partners benefit. The ants don’t seem to get anything from Phintella’s presence. They don’t suffer either, so it’s not parasitism. Instead, Phintella is more of a commensal—a creature that benefits by living alongside another, without offering any advantages in return.

It’s also not the only jumping spider to have a connection with ants. Some eat them. Others mimic them to a spectacular degree. One mimics ants to avoid being eaten by spiders so that it itself can eat spiders. And Phintella, which neither looks like an ant nor eats them, lives alongside ants and avoids being eaten by them so it can also avoid being eaten by another type of spider, which ants can eat. Ain’t nature grand?

Reference: Nelson & Jackson. 2014. Timid spider uses odor and visual cues to actively select protected nesting sites near ants. Behav Ecol Sociobiol. http://dx.doi.org/10.1007/s00265-014-1690-2

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Spider Webs Reach Out To Flying Insects. Cool, But So What?

Spider webs turn the airways of fields and forests into a gauntlet of traps. Once spun, these silken snares lie in wait for insects to blunder into them. But they’re not entirely passive. Victor Manuel Ortega-Jimenez and Robert Dudley from the University of California, Berkeley have shown that in the moments before a bee or fly careens into a web, the web reaches out to meet its victim.

Bees and other flying insects frequently collide with microscopic mid-air particles like dust and small molecules. These strip electrons from their cuticles—their outer shells—leaving them with a positive electric charge. In this way, a flying bee can build up a voltage of up to 450 volts.

We’ve known this since at least 1929, but a handful of studies published this year have shown how important the electric world of insects can be. Pollen, which is usually negatively charged, can fly over to a bee before it lands on a flower. Daniel Robert showed that bees can even sense the electric fields of flowers and use them to tell which blossoms they’ve recently visited. And Uwe Greggers found that they might be able to move each other and communicate with their own electric fields.

So, if electric charge can influence an insect’s relationships with its peers or its partners in pollination, what about its predators? Ortega-Jimenez started wondering about this while playing with a magic wand. The wand, one of his daughter’s toys, had ability to attract spider webs because it produced a positive charge. If it could do that, why not a bee?

The duo collected webs of the common cross spider (Araneus diadematus) from around the UC-Berkeley campus and mounted them on a horizontal stick frame, so they had a neutral charge. They then dropped dead bees, flies and aphids onto the web and filmed their collisions with a high-speed camera.

If they first imbued the insects with a positive charge using a generator, he saw that the webs’ silken threads would stretch up to meet them around 70 percent of the time. And if the insects weren’t charged before their fall, the web never moved.

The webs in the experiment were grounded and had a neutral charge. Wild ones might have a negative one—no one has ever measured that, but it’s plausible given that plants are typically negatively charged. If that’s the case, webs would be even more strongly drawn to positively charged insects than they were in this study.

Ortega-Jimenez and Dudley write that this attraction “likely increase[s] the risk of capture for free-flying prey”.

The threads only move over 1 or 2 millimetres, but the duo point out that this is similar to the gaps between them. Perhaps by reaching out to incoming insects, they might stop prey from flying between the strands.

Wait a minute, say other scientists who study the electric fields of insects. Ortega-Jimenez and Dudley haven’t made their case. Yes, webs might move towards positively charged insects, and yes, that’s interesting in itself. But so what? Would a thread that moves a millimetre closer to an insect that’s already hurtling towards a web make any difference to a spider’s success?

“The way the web bends was surprising to me, but this is what you when you buy a high-speed camera,” says Greggers. “The harder job is to demonstrate that it is relevant for the animal. Such an experiment is time-consuming but not very difficult to do. We had to demonstrate the relevance for the animal in our paper.”

Robert agrees. The team needs to check if charged insects are more likely to be captured than neutral or negatively charged ones. “As a sensory ecologist, I have to wonder whether spiders themselves can sense the charge of their webs or of insects approaching, or whether they are using their webs to measure that charge,” he says. “By extension, could bees detect the presence of a web using their electro-reception sense? I sense that were are only at the very beginning of discovering electrostatics in the living world, and the way it can be sensed and used by plants and animals.”

Reference: Ortega-Jimenez & Dudley. 2013. Spiderweb deformation induced by electrostatically charged insects. Scientific Reports. http://dx.doi.org/10.1038/srep02108

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Male spider castrates himself and gets more stamina

To become both a lover and a fighter, the male spider Nephilengys malabarensis snaps off his penis inside his partner while they have sex. He becomes better at fending off other males who try to mate with her, because his now-lightened body can fight for longer without tiring. And while he’s playing the guardian, his detached genitals can continue pumping sperm into the female. Through self-castration, he gets more stamina, and he gets more stamina.


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To study vampire spiders, build Frankenstein mosquitoes

In a swarm of buzzing mosquitoes, every insect probably looks the same to you. You wouldn’t notice that some have swollen abdomens, engorged with red blood, while others are hungry and empty. You wouldn’t differentiate between the antennae of the males (fluffy) and the females (straight). But there is one animal that can spot all of these traits, using eyes that have lower resolution than yours and a nervous system that’s far simpler.

It’s Evarcha culicivora – the vampire spider.

E.culicivora is an East African jumping spider that feeds on mammal blood. Don’t worry: it’s not going to bite you. This indirect vampire only attacks mosquitoes that have recently bitten mammals, and it’s an incredibly discerning diner.

Jumping spiders are famously fussy anyway. They sit and wait for just the right victim to come along, spotting them with large eyes and pouncing upon them with well-judged leaps. Some eat other spiders, but only eat certain species. E.culicivora stalks mosquitoes, but it only female malarial mosquitoes that have recently fed. It ignores: males; individuals that aren’t full of blood; and insects of the wrong species (including other mosquitoes).

“It is the pickiest predator that we know of,” says Ximena Nelson, who studies the spider at the University of Canterbury in New Zealand.

To be that choosy, the spider must have very keen senses. Smell clearly plays a role (the spider is drawn to the odour of both bloody mosquitoes and human feet, and they themselves smell sexier once they’ve drunk some blood). But vision is important too. Even if all scents are blocked, E.culicivora can still pounce on exactly the right kind of prey. Now, Nelson, together with Robert Jackson, has worked out the visual cues that it uses.

They confronted captive spiders with lures built from body parts of dead mosquitoes, which had been glued together in different combinations like miniature Frankenstein’s monsters. The spiders saw two lures at a time, and Nelson noted which they pounced upon. “They are easy-to-handle, patient spiders,” she says. “Being so picky, it means we can ask them questions and get answers regarding their preferences that makes it seem like they answered in English.”

Nelson and Jackson found that the spiders always went for mosquitoes with blood-filled abdomens, rather than empty or sugar-filled ones, no matter which head had been stuck on top. The head matters too, though. When given a choice between two lures with bloody abdomens, the spiders picked the one with a female head rather than the one with a male head.

To check that the spiders weren’t relying on the smell of the lures, Nelson also showed them virtual mosquitoes on a screen. Again, they were more likely to pounce on virtual prey with female antennae than identical ones with male antennae. Human eyes would find it hard to tell the difference. The spiders’ eyes (and it has four pairs) have no such problem.

Having worked out the cues it uses, Nelson and Jackson are working to build the spider’s “decision tree”: the mental steps it makes in order to decide whether to pounce or hold. For now, all we know is that these preferences are innate. No learning is required. The spider appears to be born with some mental template of the ideal mosquito.

This feat is all the more impressive because the spider’s eyes and brain are so simple. The front pair is the largest and most sensitive, but even they probably only have a thousand or so receptors. The young spiders, which are just as fussy as the adults, probably just have 300 receptors per eye.

It seems hard to believe that with so few receptors these spiders can achieve that level of visual detail,” says Nelson. She says that the spider’s receptors are packed tightly in the central part of its eye, so it might be possible for it to see in extreme detail for a small part of its visual field. It probably also processes the information from its eyes in sophisticated way, but no one yet knows how it, or other jumping spiders, do this.

Reference: Nelson & Jackson. 2012. The discerning predator: decision rules underlying prey classification by a mosquito-eating jumping spider. Journal of Experimental Biology http://dx.doi.org/10.1242/jeb.069609

Images all by Robert Jackson

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Male spider snaps off own genitals inside female to fertilise her remotely, while being eaten

If your partner is likely to devour you after sex, snapping off your genitals inside her might seem a reasonable reproductive strategy. This game plan is used by males of the orb-web spider Nephilengys malabarensis and, it turns out, continues to work in their favour, regardless of whether they survive the encounter.

Thus begins my new piece for Nature News. Honestly, I can’t believe they let me keep the lede. Here’s more:

Daiqin Li at the National University of Singapore and his colleagues studied the species and found that after the male breaks away his severed organ continues to pump sperm into the female. This allows him to fertilize her remotely, while denying entry to other males. Even though the male cannot regrow his genitals and so renders himself sterile, he increases the odds that he will father the offspring of his one and only mate.

Male spiders deliver their sperm through a pair of structures known as palps, which are found on the sides of their heads. By serving sexual encounters between 25 pairs of virgin N. malabarensis, Li’s group found that every coupling ended with damage to the male’s palp. In 12% of cases it was partially severed; in the rest it snapped off completely.

Li thinks that this bizarre strategy, found in only two spider families so far, evolved to counter the female’s penchant for cannibalism. “The females are very aggressive and 75% of them kill the males during sex,” he explains. “The duration of copulation is also very short, and the females initiate the break-off.”

By dissecting the mated spiders, Li and his co-workers found that the palp has dispensed only about one-third of its sperm by the time the female pushes the male off. But it continues to transfer sperm after it breaks off, and does so at a faster rate.

And head over there for the rest of the story.

(In the picture at the top, the bigger female devours the smaller male while his palp clings on to her underside (in the red box).)

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Jumping spiders use blurry vision to judge distance

We don’t like blurry vision, and we go out of our way to correct it with glasses and contact lenses. But some animals aren’t so fussy. The jumping spider not only tolerates blurry images, it deliberately produces them.

Jumping spiders, as their name suggests, leap onto their prey from afar. They judge their jumps using the two huge (and rather beautiful) eyes on the front of their faces. And to gauge how far away their targets are, they use special retinas that produce sharp images and out-of-focus ones at the same time.

Other animals have many different ways of judging depth, but none of them apply to jumping spiders. Humans mostly rely on our two eyes. Each gets a slightly different view of the world and our brain uses these differences to triangulate the distance to objects in front of us. But this ‘binocular vision’ only works if the two eyes see overlapping parts of the world. Those of jumping spiders do not.

Chameleons can judge distance by sensing how much they have to focus their eyes to bring an object into sharp relief.  But jumping spiders have no way of actively focusing their eyes. Finally, some insects judge distance by shaking their heads from side to side, which makes nearby objects move further across their field of view than far ones. But jumping spiders can accurately pounce onto their prey without moving their heads.

Without any of these three methods, how could they possibly gauge their precise killing pounces with any sort of accuracy? Takashi Nagata from Osaka City University has the answer.

Each of the front eyes has a unique staircase-shaped retina, with four layers of light-sensitive cells lying one over the other. By contast, our retinas only have one such layer. Scientists have known about the staircase retinas since the 1980s, but Nagata has finally shown exactly what they do.  He found that the top two layers are most sensitive to ultraviolet light. The two on the bottom have a penchant for green.

And that’s a bit odd. The way the layers are stacked means that green light only ever focuses sharply on the bottom one (layer 1). Blue light focuses on the one above it (layer 2), but those cells aren’t sensitive to blue. Instead, they see the world in fuzzy out-of-focus green.

Nagata thinks that this fuzzy vision isn’t a bug; it’s a feature. The amount of blur depends on an object’s distance from the spider’s eye. The closer it is, the more out of focus it is on the second retina. Meanwhile the first retina always gets a sharp image. By comparing the images on both layers, the spider can gauge depth with a single unmoving eye.

To test this idea, Nagata placed Adanson’s house jumpers in a special arena where they had to leap at prey. If the arena was flooded with green light, the spiders made accurate jumps. If Nagata used red light of equal brightness, they fell short of the mark. Nagata even created a mathematical model for the spider’s eye to predict how far it would miss its jump under different wavelengths of light. The model’s predictions matched the animal’s actual behaviour.

Humans actually do something similar. We can use the blurry nature of background images to get a sense of distance, even if all other cues are removed. Indeed, photographers often use blurry backgrounds to create a greater sense of depth. But this is just one of the tricks we use to judge depth, and perhaps a minor one. For the jumping spider, it seems to be the only trick in the playbook.

Reference: Nagata, Koyanagi, Tsukamoto, Saeki, Isono, Shichida, Tokunaga, Kinoshita, Arikawa & Terakita. 2011. Depth Perception from Image Defocus in a Jumping Spider. Science http://dx.doi.org/10.1126/science.1211667

Photo by Alex Wild

The eyes have it – a tour through the stunning world of animal eyes

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Genetically engineered silkworms with spider genes spin super-strong silk

In a lab at the University of Wyoming, some silkworms are spinning cocoons of silk, just as every silkworm has done for millions of years. But these insects are special. They have been genetically engineered to spin a hybrid material that’s partly their own silk, and partly that of a spider. With spider DNA at their disposal, they can weave fibres that are unusually strong and tough. It’s the latest step in a decades-long quest to produce artificial spider silk.

Spider silk is a remarkable material, wonderfully adapted for trapping, crushing, climbing and more. It is extraordinarily strong and tough, while still being elastic enough to stretch several times its original length. Indeed, the toughest biological material ever found is the record-breaking silk of the Darwin’s bark spider. It’s 10 times tougher than Kevlar, and the basis of webs that can span rivers.


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Spiders coat their silk with an ant-repellent

Spider webs are great at catching flying insects, but they’re an inviting target for walking ones. The spider sits pretty in the middle of its home, surrounded by the pre-packaged morsels of the insects it has caught. It’s an all-you-can-eat buffet, and ants should easily be able to raid it. Ants are excellent predators, they hunt in large numbers, and they can negotiate their way along the non-stick parts of the web. And yet, there are very few reports of ants successfully pillaging spider webs. Why?

Shichang Zhang has found one possible answer: some spiders lace their silk with an ant-repelling chemical. Their sticky webs, which so effectively trap some insects, can also deter others.


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Spider-slayer uses ninja stealth, unbreakable grip and body armour

Spiders can tackle all manner of prey, from insects to fish to birds. But some of them specialise in killing their own kind. Palpimanus gibbulus and Palpimanus orientalis are two such spider-slayers, and they use special adaptations to tackle their dangerous prey, including ninja-like stealth, blinding-fast strikes, unbreakable grips, and heavy body armour.

Stano Pekár from Masaryk University in the Czech Republic confirmed that these two species (hereafter known as Palpimanus) are indeed specialist spider-hunters. They pounce upon a wide variety of other species and attack spiders more often than insects like flies or crickets. Using high-speed video cameras and staged battles, Pekár revealed their killer technique.


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Does Whatever a Spider Can – A Gallery

There are around 40,000 species of spiders and they have a range of incredible adaptations to hunt their prey, move about and defend themselves. This gallery explores their behaviour, from vegetarian spiders to venomless ones that crush their prey to social ones that spit venom. Arachnophobes beware.

By Robert Whyte

Most spiders kill with venom, but the uloborid spiders (such as Philoponella vicina) have lost their venom glands entirely. Instead, they kill their prey by using their silk as a murderous garbage-compactor. Once an insect lands in a P.vicina web, the spider rushes over and starts wrapping. It uses 10-20 lines of silk at once and cocoons its prey in over 140 metres of the stuff. This silken shroud compresses insects with such force that it breaks their legs, buckles their eyes, and crushes their internal organs. Once the insect is dead, the spider regurgitates digestive juices all over the silk and sucks up the fluids that remain, leaving behind a dry, hollow shell. (Photo by Robert Whyte)

More: The spider that crushes its prey with 140 metres of webbing

By Ingi Agnarsson, Matjaž Kuntner, Todd A. Blackledge

The largest web in the world belongs to Darwin’s bark spider from Madagascar. It weaves its gargantuan trap over entire rivers and lakes. The main thread can be as long as 25 metres and the sticky core can be as large as 2.8 square metres. Darwin’s bark spider also uses the toughest silk of any species. It’s twice as elastic as any other spider silk and it can resist 10 times more force than Kevlar before rupturing. It’s not just the apex of spider silk – it’s the toughest biological material ever found.

More: A spider web that spans rivers made from the world’s toughest biological material

By Ximena J. Nelson and Robert R. Jackson

The dark-footed ant-spider Myrmarachne melanotarsa is a liar. It’s a jumping spider that impersonates ants. It certainly looks the part, but it boosts the illusion with a social streak. To mimic the large societies of ants, the ant-spider travels in groups and lives in silken apartment complexes, with hundreds of individuals staying in nests connected by silk. This act protects the ant-spider from larger spiders that might eat it. It also allows the ant-spider to raid the nests of those same larger spiders. The would-be predators run away and abandon their eggs and youngsters to the charlatans. The ant-spider is a spider that looks like an ant to avoid being eaten by spiders so that it itself can eat spiders.

More: Spiders gather in groups to impersonate ants and Spider mimics ant to eat spiders and avoid being eaten by spiders

Photo by Alejandro Soffia Vega

While most spiders need to bite their prey to inject venom, Scytodes spiders can spit a sticky, venomous fluid that both traps its victims and poisons them – that’s why they’re called spitting spiders. Worse still, they do this in packs. After hatching, the spiderlings spend their early lives on their home web and they spit at, bite and devour prey en masse. As they grow up, their cooperative streak fades and they start turning on each other, cannibalising each other if they get the chance.

More: Singaporean spiders spit venomous glue, work together, eat each other

By Roland Jackson

In Kenya, there lives a spider that drinks human blood. But fear not – Evarcha culicivora is an indirect vampire. It’s after mosquitoes that have fed on mammal blood. Evarcha specifically targets malarial mosquitoes that have just fed on blood, and it can tell them apart from other similar insects using its keen senses of vision and smell. Evarcha also sniffs its way to places where mosquitoes are likely to gather and it’s bizarrely drawn to the smell of human feet. Once it feeds, the blood doesn’t just nourish the spider – it’s also an aphrodisiac. After feeding on mosquitoes, Evarcha smells sexier.

More: Drinking blood makes vampire spider sexier and Vampire spider drawn to the smell of human feet

By Trachemys

The notorious black widow spins two very different sorts of webs. The basic design consists of a horizontal sheet with vertical lines underneath, stuck to the floor with blobs of glue. These threads are incredibly taut. If an insect blunders into them, they break, stick to the insect and catapult it into mid-air, where the spider can kill it leisurely. This structure is only woven by hungry spiders. Well-fed ones spin a more chaotic tangle of non-stick threads. It’s a completely different design and akin to a silken fortress, providing the spider with better defences when it has already ensnared its fill of food. The black widows might even change the architecture of their lairs to stop themselves from overeating.

More: Death-trap or fortress – the two web designs of black widow spiders

By Matjaž Kuntner Jonathan A. Coddington

In the forests of South Africa lurks the world’s largest web-spinning spider, Nephila kowaci. It’s a giant among a family of giants. The male is no bigger than a large house spider but the female has a body that’s 3-4 centimetres long and legs that are each 7.5cm long. It was first discovered in 1978, but it took 25 years and several failed expeditions to find another, lying unsuspectingly in an Austrian museum. Three more were found shortly after in the wild.

More: World’s largest web-spinning spider discovered in South Africa

By Milan Řezáč

Sex is not a pleasant experience for a female Harpactea sadistica. After a brief dance, the male bites her and, with rotating motions, drills a needle-sharp penis into her belly. He ignores her genital opening and ejaculates directly into her body. For good reason, this style of sex (also practiced by bedbugs) is known as traumatic insemination. Normally, the last male that mates with the female would fertilise her eggs – his sperm would flush out those from previous mates. But males of H.sadistica bypass that competition by taking a more direct approach.

More: Traumatic insemination – male spider pierces female’s underside with needle-sharp penis

By Roger Seymour and Stefan Hetz

The diving bell spider is the only member of its group to spend its entire life underwater. It carries bubbles from the surface and traps them beneath a dome-shaped web, spun between underwater plants. The bubble acts as a home, a nursery, and even a gill. It automatically replenishes its own oxygen, sucking in the gas from even the most stagnant of water. As a result, the diving bell spider can stay inside for a full day before needing to top up its air supply.

More: The diving bell and the spider

By Christopher J. Meehan et al

Bagheera kiplingi is the only vegetarian spider out of around 40,000 species. It exploits a partnership between ants and acacia trees. The ants defend the trees, which repays with hollow thorns for shelter, and nutritious nodules for food. These are called “Beltian bodies” and B.kiplingi has learned to steal them, using stealth, powerful jumping legs and silken safety lines to avoid being attacked. The Beltian bodies make up the majority of its diet, but no one knows how B.kiplingi copes with them. They’re high in fibre and spiders cannot chew their food; they only “drink” prey that has already been liquefied by their venom.

More: Bagheera kiplingi – the mostly vegetarian spider


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The diving bell and the spider

In the days before scuba tanks, people used to explore the underwater world with the aid of diving bells. These large open-bottomed chambers were dunked into the water, and divers used the air trapped inside them to breathe. The bells have been around since at least the time of Aristotle, but in the rivers and lakes of Europe, one animal has been using similar structures for far longer – the diving bell spider.

The diving bell spider is the only member of its group to spend its entire life underwater. But it still needs to breathe air, and it does so by building its own diving bell. First, it spins a dome-shaped web between underwater plants. Next, it rises to the surface and traps bubbles using the fine hairs on its legs and belly. It carries them down to its web and releases them, gradually filling the dome with air. After a few trips, the spider has amassed a bubble so large that it can fit inside.


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Tarantulas climb by shooting silk from their feet

If Spider-Man really could do “whatever a spider can”, he ought to shoot webs from somewhere less salubrious than his hands. All spiders spin silk from their rear ends, using special organs called spinnerets. But one group – the tarantulas – can also shoot silk from their feet, and they use this ability to climb up sheer vertical surfaces.

Tarantulas have been kept as pets for decades, but their silk-spinning feet were only discovered in 2006 by Stanislav Gorb from the Max Planck Institute. Gorb watched Costa Rican zebra tarantulas climbing up glass plates, and saw that they left behind silken footprints – dozens of fibres, just a thousandth of a millimetre wide.

As the spider climbs, four of its legs leave the glass plate at any one time. As the legs land, they begin to slip but small nozzles secrete a viscous silken fluid that rapidly hardens and adheres to the surface. The silk acts as a tether, firmly holding the spider to the pane.


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Vampire spider drawn to the smell of human feet

In Kenya, a vampire spider is hunting down its prey by tracking the smell of human feet. If that sounds nightmarish, don’t panic – the spider Evarcha culicivora is only an indirect vampire. It’s not interested in attacking humans; it’s after mosquitoes that have fed on mammal blood. If anything, the spider is our ally – it kills female Anopheles mosquitoes that spread malaria.

Robert Jackson from the University of Canterbury discovered the spider in 2003. He quickly showed that it likes to target malarial mosquitoes, especially those that had just fed on blood, and it can recognise them based on either appearance or smell. And in 2009, Jackson, together with his colleague Fiona Cross, showed that the blood is both an aphrodisiac and a meal for the spiders. When they’ve drunk their fill, they become more irresistible to the opposite sex.

Now, Cross and Jackson are back with a new study, which shows that Evarcha likes to hang around humans. After all, what better place to find a blood-filled mosquito than the source of the blood?

The duo wafted the scent of human socks into test tubes occupied by captive spiders, which could leave at any time. They were more likely to stay if the smell came from a sock that a human volunteer had worn for 12 hours beforehand. The scent of unworn sock was less attractive. They spent anywhere from 15 to 30 minutes longer sampling the fragrance of feet, and spiders both male and female, young and old, behaved in the same way.

Evarcha’s keen sense of smell is unusual for a jumping spider, a group that’s better known for their exceptional eyesight. It’s possible that its sense has evolved to mirror that of its prey. Both the mosquitoes and the spiders are drawn to the smell of humans, in search of mouthfuls of blood. The only difference is that the mosquito takes it from our bodies and the spider takes it from the mosquito.

Reference: Cross & Jackson. 2011. Olfaction-based anthropophily in a mosquito-specialist predator. Biology Lettershttp://dx.doi.org/10.1098/rsbl.2010.1233