Is there anything a caterpillar can do to cause a bird, one of its biggest predators, to duck for cover? If your answer is no, think again and read on. (If your answer was yes, congratulations you are very, very smart, but read on anyway).
Caterpillars are a great example of defense mechanisms at work. These slow moving, relatively vulnerable creatures have a wide variety of defense strategies. Primary defenses are aimed at preventing a predator from ever becoming aware of the caterpillar’s presence. These include things like camouflage, limiting foraging times, staying on the underside of leaves or physically removing evidence of their presences by cutting leaves. When their primary defenses fail, caterpillars have an arsenal of secondary defenses. These can be chemical (tasting bad), physical (stinging spines and hairs) or behavioral (thrashing, mimicking other creatures, retracting portions of their bodies to appear larger).
Now, according to new research, we can add whistling to the list of secondary defenses, at least for the North American walnut sphinx caterpillar (Amorpha juglandis; 1). Although defensive sounds are hardly unusual in the insect world, we usually associate them with hard-bodied insects that have many mechanisms for producing sound. The study described by Bura et al. found that the sounds produced by the walnut sphinx caterpillar were done so using a method of sound production never before described in caterpillars; the forceful expulsion of air through the spiracles. In other words, the caterpillars whistled through their spiracles when threatened. Continue reading “Caterpillars Whistle, Warblers Go Hungry”