Pupae, the life stage in insects when undergoing transformation, are brown, 6.5 mm long and oval shape. Adult Copsilura look very similar in its size/shape to the house-fly. Larvae are creamy colored and have black mouth hooks with three anal hooks. As adults, they have a white face and thorax containing four black stripes and reach up to 7.5 mm long. They look very similar in shape and size to the common house-fly. Organophosphates are very toxic to Compsilura but remain tolerant to synthetic insecticides like carbaryl and permethrin.
C. concinnata is ovoviviparous. In a year, approximately 3–4 generations occur (multivoltine) with an adult life span of 5–22 days. The parasitoid larvae typically survive winters in host larvae; so since the gypsy moths overwinter as an egg, it has to find alternative hosts to overwinter in their larvae. After mating has occurred, the adult females look for host larvae. If a host meets her satisfaction for her offspring, she attaches on the host’s back using her anal hooks, punctures the integument of the host with a piercing structure on her abdomen and injects a single larva into the host's midgut or body cavity. The female produces about 100 larvae. She will sometimes attack the same host multiple times. If she injects a larva directly into the host's body cavity, it will quickly migrate to the midgut and penetrate it where three larvae stages occur. Compsilura concinnata remains a larva for only 10–17 days while waiting for its host's pupation when it will emerge from its host to pupate on another substrate or soil.
The larvae typically kill their host in about 10 days. After emerging from a host, the white maggot forms a smooth, reddish brown case called a puparium around itself. During the next stage of its life cycle, the larva will molt into a pupa inside of the puparium.
What makes this parasitoid successful on numerous host-species is its ability to have a flexible life cycle. It has the ability to alter its cycle based on the host it inhabits.