Almost 3,000 green plastic caterpillars have helped scientists unmask an important global pattern.
The study, which is published today in Science, shows that it is much more dangerous to live in the tropics and at a low elevation than it is in cooler climates.
The bright green plasticine models of the caterpillars were placed in 31 different sites around the world and then retrieved up to 18 days later.
It was conducted by the Smithsonian Tropical Research Institute (STRI) in Panama, which found that insects were the driving force for predation.
“As someone who has studied insect biodiversity in the tropics for most of my life, I wasn’t surprised that insects were responsible for most of the predation observed,” said Dr Yves Basset, leader of the ForestGEO Arthropod Initiative at STRI.
In the laboratory the scientists were able to study every marking on the caterpillars to count up the number of attacks against the little critters.
The scientists were able to distinguish the nick of a bird’s beak from the teeth marks of a mouse or the paired piecing of an ant.
They found that attack rates in fact dropped 2.7% for every degree of latitude, or 111km (69 miles), that the caterpillars were placed from the equator.
Tropical sites were the most dangerous. In Greenland, the daily chances of a caterpillar model being attacked by a predator were only 13% of the odds of an attack happening at the equator.
At the highest forested site, the daily odds of a predator attack was only 24% of the odds of attack at sea level.
Attacks also dropped 6.6% for every 100 metres of elevation.
“Most previous studies that didn’t support the conclusion that predation is more intense in the tropics were pieced together from evidence gathered in different ways by different groups of people,” Dr Basset said.
“My colleagues and I were part of a team of people from around the world who all used the same method at different sites, including a few of the ForestGEO sites. We deployed many replicates of fake caterpillars, modelled after a geometrid moth, and analysed our results together.”