When in danger, whistle. It works for the walnut sphinx caterpillar (Amorpha juglandis). The fat, juicy larvae of butterflies and moths tend to be experts at predator avoidance, using camouflage, rolling themselves in leaves, and even flicking their own poop to discourage birds, frogs, and small mammals from eating them. Whistling is just another string in their bow, researchers report online this week in The Journal of Experimental Biology. When the team used forceps to simulate the peck of a bird's beak, the caterpillars forced air through the small holes on either side of their body—normally used for breathing—to produce a high-pitched whistle. When yellow warblers heard the noise, these natural enemies of the caterpillars hesitated, jumped back, or flew off. The sound may have startled them, or perhaps they found the tune indigestible.
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