美国国家公共电台 NPR Scientists Glued Fake Caterpillars On Plants Worldwide. Here's What Happened（在线收听）

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Sometimes good research can get done with a tool so simple a child could do it. For instance, scientists around the world recently set out thousands of fake caterpillars made from clay. NPR's Nell Greenfieldboyce explains why.

NELL GREENFIELDBOYCE, BYLINE: If you've got a preschooler at home who makes little worms out of Play-Doh, you should easily be able to imagine the fake caterpillars that scientist Tomas Roslin was putting out in Greenland. He wanted to know a little critter's risk of getting eaten. And this is an old technique.

TOMAS ROSLIN: Somebody came up with it, like, decades ago.

GREENFIELDBOYCE: He says of a bird or lizard or whatever tries to bite the caterpillar, telltale beak or tooth marks get left in the soft clay. Trouble is, at his research sites up north, it wasn't working.

ROSLIN: We tried it one summer, and very few of them ever got eaten.

GREENFIELDBOYCE: He's a researcher at the Swedish University of Agricultural Sciences, and he talked about his problem with another scientist, Eleanor Slade at the University of Oxford.

ROSLIN: My friend Eleanor told me that, oh, she has been using the same technique in Borneo, and everybody gets eaten.

GREENFIELDBOYCE: The pair realized that maybe the risk of getting eaten, at least if you're a caterpillar, is actually higher in the tropics than near the poles. To test this idea, they enlisted 40 researchers in 21 countries from the Arctic Circle to southern Australia, including Liz Nichols, a biologist at Swarthmore College. She was doing research in Brazil.

LIZ NICHOLS: And then a box arrived with bright green gummy-looking caterpillars.

GREENFIELDBOYCE: Her team glued them onto leaves using glue and instructions that came in the box. A few days later, they shipped them back to a central lab.

NICHOLS: I mean it sounds kind of like child's play, I realize. 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.

GREENFIELDBOYCE: Biologists Will Petry with the Swiss Federal Institute of Technology set out his dummy caterpillars at field sites in California. He was eager to be part of this study.

WILL PETRY: We've known for a really long time that there are more species in the tropics than there are in polar regions, but we don't have as good an idea of the geography of interactions between species.

GREENFIELDBOYCE: What the scientists found was a striking pattern. If you're a caterpillar at the equator, your chance of getting attacked by a predator is much higher than it would be if you were closer to the poles - about eight times higher. Petry says all of this could help explain why certain creatures do what they do.

PETRY: There are some migratory butterfly species like the monarch, and one reason that they might migrate could be to avoid predators.

GREENFIELDBOYCE: A detailed analysis of these results, a far cry from child's play, appears in the journal Science. Nell Greenfieldboyce, NPR News.