Well, it may not be smoking, but it’s whistling. According to MSNBC science news, researchers have found that the walnut sphinx moth caterpillar (Amorpha juglandis), can make whistling noises by forcing air through its external breathing holes (“spiracles”). The paper, by Bura et al., is in the December issue of the Journal of Experimental Biology.
To confirm their idea, researcher Veronica Bura at Carleton University gently applied latex over all eight pairs of the caterpillars’ abdominal spiracles and then uncovered each pair systematically while pinching the larva. The whistles definitely came from the eighth pair, generating trains of whistles lasting up to four seconds each, and spanning frequencies that ranged from those audible to birds and humans up to ultrasound.
Why do they do this? The video below gives one clue, showing that they whistle when they’re attacked (they also thrash about):
Video of whistling caterpillar.
To test this theory, Bura et al. exposed caterpillars to a bird predator, a trio of yellow warblers (Dendroica petechia). When attacked, the caterpillars produced sounds (and thrashed), and the birds were scared off, even when they attacked for a second time. None of the test caterpillars were injured. The authors conclude that the sound is a key part of the caterpillar’s anti-predator defenses. I find this intriguing but unproven, since the authors apparently didn’t do the required controls in which birds attacked caterpillars whose whistle had been silenced by occluding their eighth spiracles (as another control, they could just occlude the seventh pair of spiracles, which also help breathe but can’t whistle). The sound, then, may play some role or no role (it could, after all, be the thrashing that scares off birds). More work is needed here!
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Bura, V. L., V. G. Rohwer, P. R. Martin, and J. E. Yack. 2010. Whistling in caterpillars (Amorpha juglandis, Bombycoidea): sound-producing mechanism and function. J. Exp. Biol. 214:30-37.
I always thrash and whistle when attacked by birds. Well, almost always.
Of course: is it the thrashing, the whistling, a combination, or something else? Research controls are just like troubleshooting. You have to eliminate all the coincidences and get to the cause.
btw- I prefer a Sennheiser e825S microphone for recording caterpillars.
hypothesis
You post some great stuff here!
I would have guessed the caterpillars were making a sound similar to that of something that likes to eat their predators. Kudos pointing out the need for controls.
Yeah, but can it whistle “Melancholy Baby”?
Wondering why they use Bombycoidea in the title? When I read the note in the e-mailing there were no pictures included, and I skipped to the experimental procedure without reading the introductory paragraph and without really training on the caterpillar species. Seeing Bomybycoidea in the title, I just assumed the subjects were silk moths (my sloppiness). Then a friend pointed out the discrepancy: the sphinx moths are in the superfamily
Sphingoidea. How could a mistake like this be published by the Journal of Experimental Biology? You’d think I was the proof reader.
Whistling caterpillars…hmmm, could be the name of a band.
Or a movie,
“Whistling caterpillars, dancing spiders”