Here are photographs of a clump of ectoparasitic larvae I found attached to a small caterpillar. I think they are wasps in the genus Euplectrus (Eulophidae). Females apparently inject hosts with a venom that prevents the caterpillar from molting, thus preventing the caterpillar from shedding the larvae along with the discarded skin. Caterpillar was approximately 12 mm in length. Media, PA.