Why Do Caterpillars Shake When You Scream?

February 15, 2024

With the exception of loud cries made by the sphinx moth caterpillar during its larval stage, insects aren’t exactly noisy creatures. But some caterpillars, like the hawk moth and Nessus sphinx caterpillar shown above, have been known to make high-pitched sounds when they feel threatened by predators. It turns out that the caterpillars are able to elicit these shrieks thanks to a process taking place in their guts. The caterpillars contract muscles in their upper guts, which causes air to be forced through a constriction inside them. This produces the high-pitched noises, which are strongest around the caterpillar’s mouth parts.

The caterpillars also have other ways to react to loud noises, including writhing their bodies and shaking their heads. This is a result of a reaction to physical disturbances in their environment rather than to the sound itself. It’s like when you slam your finger into a door and it rattles, or if you shake your head when someone yells at you.

Caterpillars are known to use these calls as a defense mechanism against parasitic flies. They’re able to hear the sounds of the flies, which are produced at a frequency that’s close to the caterpillars’ own shrieks, so the caterpillars recognize these sounds as an attack and respond accordingly.

Researchers have also found that the sphinx caterpillar’s cries are effective at scaring off birds. Jessica Lindsay, an undergraduate student from the University of Washington, recorded the sphinx caterpillar’s sound and played it back to wild Black-capped Chickadees at feeders. The Chickadees responded as if they were hearing a real seet call, indicating that the caterpillar’s shrieks do indeed scare off predators.

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