A team of researchers glued fake caterpillars on habitats around the world to discover predation patterns. They glued thousands of tiny clay caterpillars to plants in 31 sites across the six continents, from the Arctic Circle to Australia.

The fake worms were designed to tempt insect-eating predators. After the international team of researchers had retrieved their caterpillar at sites in both hemispheres, they discovered an unusual pattern: even when a caterpillar is fake, it stands at much higher chance of being eaten if it’s closer to the equator or at lower elevations.

Fake Caterpillars
The researchers were even able to tell if the predator that “attacked” the fake caterpillar was an insect, bird or mammal, telling by the marks left in the soft clay. Image credit: Chung Yun Tak.

Fake caterpillars helped assess predator behaviors across the globe

It’s a known fact that biodiversity is greater in ecosystems that are near the equator, but scientists in the new study set out to discover how that might affect predation danger, compared to other ecosystems where biodiversity is lower. They decided that the best way to assess it was using artificial caterpillars.

The idea was originally from researcher Tomas Roslin at the Swedish University of Agricultural Sciences and the University of Helsinki in Finland. Roslin was using fake caterpillars to lure predators in Greenland, to study predation risk in the area.

Fake Caterpillars
Researchers used caterpillars made of modeling clay. Image credit: Saskya van Nouhuys.

However, Roslin wasn’t having any luck, as the predators weren’t attempting to eat the fake caterpillars. He discussed the problem with his colleague Eleanor Slade at the University of Oxford, who told him she had a lot of success with the dummy caterpillars when she used them in rain forests in Borneo. They both realized that a caterpillar’s risk of being eaten possibly vary around the world. The pair then asked scientist friends around the world to help them with the fieldwork.

“I mean, it sounds kind of like child’s play, I realize,” said researcher Liz Nichols of Swarthmore College, according to NPR. “But this kind of massive, simple, standardized technique is really powerful when you can implement it at a global scale in a really well-replicated way.”

Predation pattern shifted depending on latitude and altitude

The caterpillars were created from a tool resembling a garlic press, according to Roslin. A total of 41 scientists from 21 countries helped with the research. The researchers took the plasticine “inchworms” in protective tubes and glued them to plants across the world, for periods of four to 18 days. The fake caterpillars were then retrieved to see if they showed signs of being attacked by predators.

Fake Caterpillars
This minuscule fake caterpillar was attacked by a bird. Image credit: Tapani Hopkins.

“We’ve known for a really long time that there are more species in the tropics than there are in polar regions,” said Will Petry, a biologist with the Swiss Federal Institute of Technology who was part of the research team, according to NPR. “But we don’t have as good of an idea of the geography the interactions between species.”

Petry admitted that’s why he was eager to work in the study. He was conducting an investigation in California when the dummy caterpillars arrived in the mail. He took them and glued them onto plants, including cacti, and then he left them there for a few days. After some time passed, he carefully placed them into individual tubes, to preserve any bite marks in the plasticine clay, and mailed back the caterpillars to the lab in Helsinki, Finland.

Nichols also received a box full of the fake caterpillars, and colleagues helped her glue them on plants at her research sites in Brazil. Researchers estimate that over 3,000 dummies were deployed at 31 sites around the world. They found that not only the risk of predation decreased at the poles but that the risk increased at lower elevations. Roslin noted that if you go up a mountain slope at the equator, you would also find a decrease in danger of getting eaten. The researchers concluded that the pattern was mostly driven by small predators like ants rather than mammals or birds.

The findings revealed that more types of species near the equator do equate to more mouths to feed, said the researchers. Roslin told Live Science he was amazed when he saw the data.

“I simply jumped out of my socks,” said Roslin, according to Live Science. “There was the pattern – and not vague, but entirely clear!”

There was another discovery for the researchers, as a colleague who was reviewing their study suggested testing to find whether the pattern held up across changes in elevation in habitats in addition to across latitudes. They found the same pattern, as the odds of predation dropped by 6.6 percent with every 328-foot (100 meters) increase in elevation.

Roslin noted that the findings highlight the importance of large-scale comparative studies analyzing how species engage with each other, to better understand the individual and group dynamics of animals in a range of habitats.