Bees vs. Hornets Couzin wants to go to Japan to see one of the most extreme examples of swarm behavior. T ere, a giant hornet buzzes through the air. It finds a beehive and marks the hive with a chemical smell to call other hornets to a feast. When these hornets attack, the honeybees


don’t stand a chance. Each hornet is five times larger and 20 times heavier than a bee. Each can rip apart 40 bees a minute. T e hornets carry the honey and larvae back to their nest. T ings don’t always go well for the scout


hornet, though. Biologist T omas Seeley, who studies bee swarms, has observed how the bees fight back. If a honeybee sees the scout, it turns its body to keep the hornet in sight. T en it releases a chemical message of its own. Danger! T e other honeybees pick up the warning with receptors in their antennae. T e honeybees swarm. Hundreds surround


the hornet. T en the honeybees start to shiver and shake. T is motion makes heat. Inside the bee swarm, the hornet fights back. It attacks and kills the closest bees. T e bees don’t stop, though. T ey push dead bees out of the swarm. Other bees take their place and start to shiver. Soon, the temperature inside the bee swarm


rises above 47°C. T e bees can stand the heat. T e hornet can’t. It cooks to death. Now, it can’t tell other hornets about the hive. T e honeybees have saved the hive.


Lots of Locusts In Africa, Couzin has discovered the secret of locust swarms. Normally, these insects avoid one another. Yet when food is scarce, they start to crowd together. T ey bump into one another T is touch sends a message to their brains.


T at releases a chemical that sets off a series of changes. T e locusts’ green bodies turn black with red eyes. T ey grow wings and become aggressive. T ey start marching, then flying. T e reason why stunned Couzin. He saw a


locust catch up to one in front of it. T en it bit the locust! It turns out the locusts in back are trying to catch the ones in front—to eat them. T e ones in front are trying to escape. “T ey turn on each other,” Couzin says.


T e locust swarm “looks cooperative. It’s really a forced march driven by cannibalism.” T e locusts’ sense of touch keeps them moving.


Swarm Secrets T e locusts are just trying to stay alive and find food. Other animals may swarm to stay safe. Yet all of these animals are reacting to changes in their environment. Smells, pressure, and other sensory inputs


trigger this swarm behavior. T en nerves race messages to brains. Soon, hundreds, thousands, even millions of individuals begin to act as one. T is swarm behavior fascinates Couzin. “I


could watch swarms for ages,” he says. Who knows what other swarm secrets he’ll discover.


8


Giant hornets attack a honeybee hive.


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