Four Unusual and Amazing Ways That Insects Team Up
The invertebrates create elaborate structures to escape danger and shimmer in synchronized performances to confuse predators
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When a harvester ant scurries into a hole in the ground, it enters a labyrinth of hallways and rooms it helped build that can extend many feet into the earth. Insects are known for their feats of engineering, such as burrowing tunnel systems into the ground or assembling hexagonal homes coated in honey. Scientists have long marveled that tiny-brained individuals create these ambitious projects. “Insects are very underrated,” says Mizuki Uemura, an entomologist at the University of Queensland in Australia. “People think they’re dumb and there’s not much to them, but there’s so much more to learn from them.”
Insects work together in many ways to accomplish awe-inspiring endeavors that often go under the radar. To learn more about the stranger feats of teamwork these invertebrates pull off, we scoured the scientific literature and called up four insect experts. Here are some of our favorite cooperative insect actions.
1. Fire ants clump up into rafts
When it floods, fire ants can form living carpets that float for weeks. They hoist their precious queen and the colony’s larvae on top of the mats to transport them safely to land.
Fire ants live wherever it’s warm and humid. Today, you can see invasive fire ant rafts floating atop floodwaters in places like Texas and Louisiana. In the 16th century, Spanish ships accidentally carried the South American species around the world. To survive frequent floods in the Amazon rainforest, they evolved to evacuate their land-based colonies and paddle until they find a suitable home. The ants bind together in a giant squirming layer that looks like “living fabric,” says Hungtang Ko, a mechanical engineer at Princeton University who studied the animals while earning his doctorate at the Georgia Institute of Technology.
Ko’s research demonstrates that the ants, which are waterproof but not great swimmers, float better in groups. Ants in a liquid will stick together in the same way pieces of cereal cling to each other in a bowl of milk—a phenomenon known as the “Cheerio effect.” Small objects like an ant indent the thin film on top of water, and that dimple on the surface can pull in nearby ants. Once enough ants are clumped together, they begin to optimize the shape of their raft. Sticky pads on their legs help them stack their bodies on top of each other and anchor themselves perpendicular to neighbors. The gaps created between their bodies create air pockets that help the raft float, making it harder to sink even if poked directly with, say, a stick.
Collective movement, in which ants randomly wander off the edges of a raft formed by their companions, helps the colony search for land. When they are floating, ants will often extend “arms” out from the raft. From above, the appendages look like the protuberances of an amoeba. By pushing out narrow bridges, the ants are better able to search for a place to disembark. Once they’ve found it, they use their mandibles to carry the prized queen and larvae onto dry ground.
2. Bees do “the wave” to repel hornets
Giant honeybees, one of the largest species of bees at three-quarters of an inch long, often form open nests. Instead of a layered structure, they piece together a single comb, which can be several feet across, whose surface is enveloped front and back by hundreds of golden-brown individuals. The open structure means they don’t have to find places like rare tree hollows that are popular with other animals; they can nest in any sturdy tree branch or on an ideal cliff’s edge. Unfortunately, this type of home leaves them exposed to potential predators. Wasps and hornets, which like to eat the giant bees, can head straight to the hive and attack.
But the colony has a special technique to defend against predatory insects: shimmering. When a wasp-sized predator passes by the nest, the wall of bees will glitter in repeated waves of activity. Each quiver lasts only a fraction of a second. Gerald Kastberger, a retired bee biologist at the University of Graz in Austria, compares the movement of the bees to a coordinated wave of people standing in a stadium. “You have to watch your neighbors,” he says.
When faced with the shimmering curtain of bees, some predators head the other way. Large displays often cause a hornet to flee, for example. The fast-moving patterns might also startle larger predators like mammals or birds.
The hive relies on “trigger bees” to start the wave, Kastberger says, much as stadium waves rely on enthusiastic fans to start the first section of a movement. Clinging to their comb, some of the giant honeybees flick their abdomens, and others follow. Research suggests a similar group of bees initiates the shimmer every time.
Waving their abdomens doesn’t just drive away intruders. Shimmering also releases pheromones that may ready the insects in case shaking is not enough. If a predator persists, colony members will descend and sting or bite their adversary until it is driven away.
3. Caterpillars stick together while creeping in single file
Moth larvae, or caterpillars, crawl long distances to find food and a safe place to spin their cocoons. In the case of processionary caterpillars, which exist in different species across parts of Europe and in Australia, they form long unbroken lines as they walk one by one over the ground or along tree trunks.
Uemura, who once researched the caterpillars, says the curious behavior may be to gain protection in numbers. The caterpillar convoy has an important defense: fluffy hairs. The bristles covering each animal are coated in proteins that can cause rashes or eye irritation in humans. If the caterpillars travel together, they might be less likely to get picked off by predators by combining defenses—and they look like a bigger organism, she says. In addition, like kindergarteners walking in single file, they might be less liable to become lost as they follow the caterpillar in front of them.
Sticking together in a train might also further help the “hairy scaries,” as they are sometimes called, when they arrive at their destination. Uemura says that with greater numbers, the caterpillars could find it easier to loosen the soil when they reach a suitable site to burrow down and produce their underground cocoons.
4. Sawfly larvae tap out messages
Sawfly larvae also travel in packs like caterpillars, but they typically move in clusters rather than in single file. One of their unusual behaviors is using vibrations to communicate with one another, which helps them stick together.
Lisa Hodgkin, who studied sawflies for her doctorate at the University of Melbourne in Australia and is now a social work researcher at Monash University, says the groups of 30 or 40 individuals sometimes scatter while feeding on a tree. If one gains distance from the group, it may lift up its little abdomen and tap it against a tree, says Hodgkin, and then pause. If the main group of insects is nearby, the rest of the swarm will start tapping like a homing signal until the separated larva returns to its companions.
The tapping is also used to initiate movement of the entire troop. Leading larvae will start to tap, and the rest of the pack will tap—and then everyone will trundle onward. This coordination helps the larvae stick together while moving along trees to find food.
Each group usually includes both leader and follower larvae, as colonies with a mix of both are better at traversing eucalyptus trees and eating more leaves. “It’s the same for humans and for any cooperating species,” Hodgkin says. “You need those leaders and followers to make a community work.”
Turnbull FL via Wikimedia under CC By-SA 3.0 / Anirnoy via Wikimedia under CC By-SA 4.0 / Christopher Watson via Wikimedia under CC By-SA 3.0 / Andreas Kay via Flickr under CC By-SA 2.0
