Saddleback caterpillar (Acharia stimulea), Newark DE, August 2018.
I’m a fan of slug caterpillars, and in the Mid-Atlantic, caterpillars become easier to find in late summer. Slug caterpillars get their name by their appearance; their heads are oriented downward and their legs are hidden beneath their bodies (the prolegs are reduced to small spines), giving them the likeness of moving like a slug.
The saddleback caterpillar is one of the more well-known member of this group, earning its name from the saddle-shaped spot that appears on its back. But what most people remember about the caterpillar are the poisonous spines that cover its body in large, urchin-like tufts, keeping birds at bay. While pretty, the sensation of the spines are akin to stinging nettle, and can last from a few minutes to hours, depending on the reaction.
(a mild reaction to the spines--which is how I knew there was a saddleback caterpillar in the tree I brushed past)
At least two generations in the Mid-Atlantic (year-round further south), with caterpillars common by July. Caterpillars overwinter as pupae.