Eastern tent caterpillar (Malacosoma americanum)

Eastern tent caterpillars are generally not well liked. They can quickly defoliate small trees and gather in repulsive, squirming  colonies. As if that weren’t bad enough, pregnant mares who accidently eat tent caterpillars are known to abort their fetuses. These facts make it even more surprising that these creatures are in fact one of the most fascinating caterpillars found on the farm.  Not only are the amazingly sociable larvae capable of building the biggest nest of any tent caterpillar, they also vomit deadly cyanide when threatened.

Their nests are engineering marvels that are carefully constructed to keep the caterpillars warm. This is important because they can’t digest their food if they get too cold. Nests are typically started where two branches divide and expanded daily with new layers of silk. The widest side of a nest often faces the morning sun to capture as much warmth as possible. After several weeks, the nests develop into a multi-chambered, greenhouse-like structures that allow the caterpillars to control their body temperature. Their habit of gathering together in a large mass is also believed to have evolved in an effort to keep warm.

Their ability to produce cyanide is partially a result of their prefered diet of cherry tree leaves. Cherry leaves – especially those from the black cherry tree – are cyanogenic and provide the caterpillar with the raw materials necessary to make the poison. As a result, tent caterpillars are threatened by few predators other than the parasitic wasps and flies who lay their eggs on unsuspecting larvae.

While undeniably destructive, the damage done by these caterpillars often does not have a significant economic impact. Infested trees are typically ornamental and quickly sprout new leaves once the larvae leave to start the next phase of their life cycle.

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