Caterpillars in Your Yard and Garden
Hag moths caterpillars (Phobetron pithecium) are present in summer and fall. They produce one generation per year.
Sometimes called the monkey slug, the full-grown hag moth caterpillar is brown, 0.5 inch long, and has nine lateral lobes or processes with urticating hairs. Some of these lobes protruding from the sides of the body are longer than others and are occasionally shed. Host plants include various forest trees and shrubs.
About the family
Slug caterpillars of the Limacodidae family have reduced thoracic legs, lack abdominal legs (replaced by sucking discs), and move in a creeping fashion. They are 0.4 to 1 inch long and may be oddly shaped. The head is often hidden under the thorax, adding to their sluglike appearance. The body ranges in color from dull to bright (green, yellow, orange, red and purple) and may be smooth or covered with elongated, stiff (sometimes poisonous) spines and urticating (stinging) hairs.