One of the most commonly found parasitoid of caterpillars (moths and butterflies) are Microgastrinae wasps (Hymenoptera, Braconidae). They are small (usually 2-5 mm long), mostly black or yellow and with a rather short "abdomen" (metasoma). Due to its narrow host specificity (i.e., a wasp species often parasitizes one or just a few related species of caterpillars) the microgastrine wasps are a key component in the biological control of agriculture and forestry pests, and have also been extensively used in biodiversity, ecological, behavioral and molecular studies. Also, they are extremely diverse, with more than 2,500 described species worldwide, and an estimate of up to 40,000 more species awaiting for description.
[This post is an expanded article based on a post from a blog on Microgastrinae wasps (http://cncbraconidae.blogspot.ca/) that used to be written by one of us (Jose Fernandez-Triana). That blog is no longer active but its contents have been moved to this website].