They develop through three instars and become 12 to 18 mm long when fully grown. Each puparium is 9 to 10 mm long and 3 to 4 mm wide. The species of blow flies covered here occur throughout the contiguous states and in many other temperate regions of the world as well. Most blow fly larvae feed in carrion or other decaying organic matter. They often infest wounds of sheep, goats, cattle, and other animals.
Unkempt sheep are particularly subject to attack.
Adult blow flies are attracted to nectar, carrion, garbage, and other refuse and soggy, bloody or soiled hair, fur, or wool. The larvae which soon hatch feed on decaying flesh or matted hair. Infested wounds often become inflamed and the hair or wool falls out. Blood poisoning may result. As a rule, most blow fly larvae do not attack healthy tissue.