|Acharia stimulea the saddleback caterpillar, Delaware|
There are two methods for finding the saddleback caterpillar. The first is careful searching of a variety of its plant hosts, looking for evidence of feeding and flipping leaves over to see the larvae. The second method is to put on a pair of shorts from 1982 and stride confidently through shrubby vegetation until you feel the caterpillar. Like many other species in the family Limacodidae, the saddleback's spines will deliver a painful sting - I have (accidentally) encountered many of them this way.
The Limacodidae are called the 'slug caterpillars' because their prolegs (the grippy legs at the rear) are modified into one big pad. Members of this group also have turtle-style retractable heads, which I think contribute to their exotic appearance. This video might show you what I mean: