Eat Up!

Life is risky for a caterpillar. At any moment, it could be snatched by a hungry beetle, bird, or lizard. But are caterpillars in more danger in some parts of the world than others? Tomas Roslin wanted to find out.

Roslin is a scientist at the Swedish University of Agricultural Sciences. He studies how predators and prey interact. He wondered if a caterpillar’s location affects its chance of being eaten. So he set up an experiment—using fake caterpillars as bait!

Life is risky for a caterpillar. A hungry beetle, bird, or lizard could eat it at any moment. But are some caterpillars in more danger than others? Does their safety depend on where they live? Tomas Roslin wanted to find out.

Roslin is a scientist. He works at the Swedish University of Agricultural Sciences. He looks at predators that eat other animals. He also looks at the prey they eat. He studies how the predators and prey act together. He wondered if a caterpillar’s location affects its chance of being eaten. So he set up a test. He used fake caterpillars as bait!

Scientists often use decoys, or fake animals, to study how frequently predators attack. The idea is simple: Set out a decoy that looks like prey, then wait to see if a predator strikes. 

Roslin decided to use fake caterpillars made of green modeling clay. If a predator tried to eat a decoy, it would leave bite marks or scratches in the clay. By comparing the number of attacks in different locations, Roslin could tell how risky each place is for real prey.

Roslin wanted to collect data all around the globe. But he knew that would be extremely difficult to do on his own. So he asked colleagues around the world for help. Dozens of people agreed to assist him.

Roslin sent decoys to each volunteer. He told everyone to put the fakes in similar spots. That way, he would know that any differences in the results were due to geographic location alone.

Some scientists want to see how often predators attack. So they set out decoys. The fake animals look like prey. Then scientists wait to see if a predator strikes.

Roslin decided to use decoy caterpillars. They were made of green clay. A predator would try to eat the fake prey. It would leave bite marks or scratches in the clay. Roslin planned to place decoys in different locations. Then he’d count the number of attacks on each. That way, he’d learn how risky each place is for real prey.

Roslin wanted to collect data from around the world. But he knew that would be hard to do on his own. So he asked other scientists for help. Dozens of people agreed. Roslin sent decoys to each volunteer. He told everyone to put the fakes in similar spots. He could compare the results that way. He’d know that any differences were due to location alone.

The volunteers planted almost 3,000 fake caterpillars in 31 places where real caterpillars live. The decoys were spread across six continents, from a forest in Australia to the frozen tundra of Greenland. 

After a few days, the volunteers collected the decoys and sent them back to Sweden. Scientists there counted the bite marks. The shape of a mark told them what type of predator had attacked. The most common predators were other insects, such as beetles and ants.

The bite marks revealed a pattern: The closer a decoy was to Earth’s equator, the more likely it was to be attacked. In fact, a caterpillar near the equator was eight times more likely to be preyed on than one near Earth’s poles. Roslin thinks that’s because more predatory insects live close to the equator. These hunting insects are more active where it’s warm.

Roslin enjoyed working with many people to gather as much data as possible. He hopes to do more global experiments soon. “Together we can achieve a lot,” he says.

The volunteers placed almost 3,000 fake caterpillars. The decoys were spread across six continents. They were set in 31 areas where real caterpillars live. These spots included everything from a forest in Australia to the tundra of Greenland.

The volunteers waited a few days. Then they collected the decoys. They returned them to Sweden. Scientists there counted the bite marks. The shape of a mark told them what had attacked the decoy. The most common predators were other insects, like beetles and ants.

The bite marks showed a pattern. A decoy closer to Earth’s equator was more likely to be attacked. In fact, it was about eight times more likely to be preyed upon than a caterpillar closer to Earth’s poles. Roslin thinks that’s because more hunting insects live close to the equator. They’re more active where it’s warm.

Roslin liked working with many people. It allowed him to gather a lot of data. He hopes to do more global experiments soon. “Together we can achieve a lot,” he says.