This is the story of a very hungry caterpillar, a very clever “zombie-maker” wasp, and a plant that makes defensive smells. It’s all real science.
Once upon a time, there was a hot link, courtesy of Science News. In that link were some happy little caterpillars, grazing away on maize plants, filling their little caterpillar mouths with crispy, crunchy leaves. But the maize leaves didn’t want to be feasted upon by the “greenish, brownish, ugly caterpillars” (rude), so it sent out a smell, like a whisper on the wind. What the smell whispered was, “Hello, friend wasp, it is I, the maize plant. I am being feasted upon by some fuzzy wuzzy caterpillars, won’t you come and make them stop? My leaves are so pretty, and now they’re dotted with caterpillar-mouth-sized holes. Do help, friend wasp!”
Now the wasp was a very clever wasp, and was also full of little wasp eggs that needed a home. So the clever wasp smelled the smell from the plants, and knew the maize plant wanted her to come. She flew like a... well, like a wasp, until she reached the smell, and there was a jolly fat caterpillar, munching away. So the clever wasp landed on the caterpillar and injected an egg into the fuzzy little thing, then flew away, smiling a devious smile.
The caterpillar kept munching as the egg got bigger, and soon out came a wasp larva. That larva was hungry too, so it started eating the very hungry caterpillar from the inside out, feasting on its maize-fueled flesh even as the caterpillar continued to eat its leaves. This went on for days, the baby wasp munching as the caterpillar “just passively stay[ed] alive longer as a source of fresh baby food.” Then the baby wasp was full and flew away, and the caterpillar was dead. Dead.
But never fear! For the other caterpillars knew about the smell-whisper. They learned that if they ate leaves that contained the plant defense compound indole, the wasps would stay away! So whenever the smell-whisper brought clever wasps to them, they switched to indole-rich leaves instead.
Indole’s “mothball-like odor [is] terrible in high dosages,” Turlings says. Caterpillars didn’t like it much either — except when female wasps were zinging around them. Then the caterpillars fed willingly enough, a test showed. “It’s almost like self-medicating,” he says.
Not all was well. The leaves made the caterpillars fat, but not healthy. Still, they didn’t get baby zombie wasps injected into them so that they could feed on them from the inside, and so they all lived happily ever after, for all of their relatively short life-spans, which can be shortened by eating indole.
Science is awesome and terrifying. The end.