These Microscopic Balls Protect Insects From Their Own Waste
The intricate soccer-ball structures in the image above are so tiny that you could pack few hundred of them into the width of a human hair. They’re probably the most beautiful non-stick coatings to have ever evolved.
These balls, known as brochosomes, were first discovered in the early 1950s. Scientists knew that they were found on the shells of leafhoppers—a group of colourful, sap-sucking insects that includes more than 20,000 species. They make the brochosomes within special glands in their guts, secrete them by the billions in a milky anal fluid, and spread them over their bodies using their legs. When the fluid dries, the brochosomes form a powdery coating, and the leafhoppers spread them even further using comb-like hairs on their legs.
Roman Rakitov from the Russian Academy of Sciences first saw the brochosomes when he put a leafhopper under a powerful microscope. His advisor (wrongly) told him: “Look, your leafhopper is coated with pollen!” “The published data on brochosomes were so scarce,” says Rakitov, “that pretty much everybody who later worked on them re-discovered much of the information about them independently.”
Rakitov became mesmerised by the brochosomes and wanted to work out what they were for—a mystery that had gone unsolved for almost 50 years. Since the 1970s, several scientists have noticed that the leafhoppers are great at repelling water, and suggested that the brochosomes might help. It was a nice idea, but Rakitov became the first to test it, with help from Stanislav Gorb from the University of Kiel.
If you put a drop of water on a table or plate, it will flatten out. The “contact angle” that it makes with the surface falls towards zero. But a leafhopper’s wing is so good at repelling water that a drop will sit upon it as a nigh-perfect sphere. It forms a contact angle of around 170 degrees—one of the highest ever recorded for a natural surface.
The brochosomes are responsible. The droplets sit upon their tips, and are cushioned by the pockets of air between them. Without these spheres to add roughness and texture, the naked leafhopper shell has a contact angle of just 120 degrees.
Other natural water-repellent surfaces like lotus leaves or guillemot eggs work in the same way, but they are made that way. The leafhoppers, however, waterproof themselves by actively applying a rough surface to their shells. There are a few other similar examples: Christoph Neinhuis from Dresden University told me about some plants that coat themselves with spores for a similar reason.
But leafhoppers are land-living insects—why do they need such good waterproofing? The brochosomes might help to repel rain, or even spider silk, but the classic explanation is that they protect the leafhoppers from their own waste. After sucking the sap of trees, these insects excrete any extra sugar as a sticky liquid. This is a serious hazard. If the liquid contaminates their shells and dries, it could stick the insect to a leaf, or glue its body parts together. Some bugs deal with this problem by shooting the waste away from their bodies at high speed. Others coat their droplets with a waxy powder. Perhaps the brochosomes are the leafhoppers’ solution?
Again, Rakitov and Gorb have tested this idea. They clipped the wings from some European leafhoppers (Alnetoidia alneti) and removed the brochosomes from half of them. They then placed the wings in a cage with 100 live leafhoppers, which rained a downpour of sticky waste upon them.
A week later, the duo found that 155 spots of dried waste had stuck to the wings, but only three had hardened on the ones with intact brochosomes. The naked wings had become dirtier; the brochosome-coated ones were almost totally clean. The duo had found strong evidence that the tiny spheres can indeed protect the leafhoppers from their own waste.
That’s one mystery down, but many more left to solve. How exactly do leafhoppers produce such intricate structures? Does their soccer-ball form make them more efficient at repelling water than other shapes? And how do they actually stick to the leafhoppers’ surfaces, and why do they often form long chains? They’re not glued, says Rakitov. “We don’t know but we plan to find out.”
Reference: Rakitov & Gorb. 2013. Brochosomal coats turn leafhopper (Insecta, Hemiptera, Cicadellidae) integument to superhydrophobic state. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2012.2391
Rakitov & Gorb. 2013. Brochosomes protect leafhoppers (Insecta, Hemiptera, Cicadellidae) from sticky exudates. Interface. http://dx.doi.org/10.1098/rsif.2013.0445
Related Topics
Go Further
Animals
- Octopuses have a lot of secrets. Can you guess 8 of them?
- Animals
- Feature
Octopuses have a lot of secrets. Can you guess 8 of them? - This biologist and her rescue dog help protect bears in the AndesThis biologist and her rescue dog help protect bears in the Andes
- An octopus invited this writer into her tank—and her secret worldAn octopus invited this writer into her tank—and her secret world
- Peace-loving bonobos are more aggressive than we thoughtPeace-loving bonobos are more aggressive than we thought
Environment
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- U.S. plans to clean its drinking water. What does that mean?U.S. plans to clean its drinking water. What does that mean?
- Food systems: supporting the triangle of food security, Video Story
- Paid Content
Food systems: supporting the triangle of food security - Will we ever solve the mystery of the Mima mounds?Will we ever solve the mystery of the Mima mounds?
- Are synthetic diamonds really better for the planet?Are synthetic diamonds really better for the planet?
- This year's cherry blossom peak bloom was a warning signThis year's cherry blossom peak bloom was a warning sign
History & Culture
- Strange clues in a Maya temple reveal a fiery political dramaStrange clues in a Maya temple reveal a fiery political drama
- How technology is revealing secrets in these ancient scrollsHow technology is revealing secrets in these ancient scrolls
- Pilgrimages aren’t just spiritual anymore. They’re a workout.Pilgrimages aren’t just spiritual anymore. They’re a workout.
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- This ancient cure was just revived in a lab. Does it work?This ancient cure was just revived in a lab. Does it work?
- See how ancient Indigenous artists left their markSee how ancient Indigenous artists left their mark
Science
- Do you have an inner monologue? Here’s what it reveals about you.Do you have an inner monologue? Here’s what it reveals about you.
- Jupiter’s volcanic moon Io has been erupting for billions of yearsJupiter’s volcanic moon Io has been erupting for billions of years
- This 80-foot-long sea monster was the killer whale of its timeThis 80-foot-long sea monster was the killer whale of its time
- Every 80 years, this star appears in the sky—and it’s almost timeEvery 80 years, this star appears in the sky—and it’s almost time
- How do you create your own ‘Blue Zone’? Here are 6 tipsHow do you create your own ‘Blue Zone’? Here are 6 tips
Travel
- This town is the Alps' first European Capital of CultureThis town is the Alps' first European Capital of Culture
- This royal city lies in the shadow of Kuala LumpurThis royal city lies in the shadow of Kuala Lumpur
- This author tells the story of crypto-trading Mongolian nomadsThis author tells the story of crypto-trading Mongolian nomads
- Slow-roasted meats and fluffy dumplings in the Czech capitalSlow-roasted meats and fluffy dumplings in the Czech capital