Subject: Help identifying caterpillar
Geographic location of the bug: Huntingdon, Pennsylvania
Time: 09:04 PM EDT
There are about 50 of these guys eating a bush in my backyard, can’t seem to ID them. Please help! Thanks.
How you want your letter signed: Andrew Sharpless
Based on this BugGuide image, you have encountered third instar Promethea Moth caterpillars. Caterpillars pass through five instars or phases prior to pupation. The first instar is marked by hatching from the egg, so your third instar caterpillars are half grown. According to BugGuide: “larvae feed on leaves of apple, ash, basswood, birch, cherry, lilac, maple, sassafras, sipcebush, sweetgum, tulip-tree (1); also recorded on buttonbush, magnolia, and other trees.” Since you did not mention the type of bush, we are guessing you have no particular investment in it (meaning we are guessing you would know if you purchased a lilac or magnolia) and that you will let them develop. Caterpillars rarely affect the health of plants they are feeding upon as leaves will generally regenerate. The adult Promethea Moths are large and impressive, though not brightly colored.