a plasticine caterpillar glistening with moisture while probing for predator attacks in the rain forest of Hong Kong
Chung Yun Tak

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Fake caterpillars reveal the worst places in the world to be prey

Living in the tropics or at low elevations is much more dangerous than living in cooler climates. That’s the conclusion of a new study with an unusual methodology: deploying bright green clay caterpillars around the world. Biologists already know that the numbers of kinds of plant and animals decreases with distance from the equator. And they suspected there might be similar trends in how species interact, but no one had studied this systematically in different places. So researchers made 2900 dummy caterpillars (pictured) that 40 colleagues placed at 31 sites at different latitudes and elevations and then retrieved 4 to 18 days later. Back in the lab, the ecologists counted up the attacks by different predators—they can tell the nick of a bird's beak from the teeth marks of a mouse or the paired piercings of ant, for example. Daily attack rates dropped 2.7% for every degree of latitude—or every 111 kilometers—north or south from the equator. As such, at the farthest spot—in the Arctic—predation was 1/8 that at the equator, the team reports today in Science. The difference was mostly in the number of attacks by arthropods, mostly ants, in the tropics. The rates also dropped 6.6% for every 100-meter increase in elevation. Though it’s not yet clear whether these trends hold for all plant eaters, that they exist at all means that ecologists need to keep them in mind as they figure out the dynamics of how ecosystems function.