Blow flies and flesh flies are very common flies associated with dead animals. Blow flies can be found in almost every known terrestrial habitat and they are found in association with human civilization throughout the world. Blow flies include a number of species including the common Blue Bottle Fly and the Green Bottle Fly. Adult flies are metallic blue, green, copper or black colored flies that otherwise resemble large house flies in appearance. Other blow flies include the Black Blow Fly and the Cluster Fly.
The larvae (maggots) of these flies feed on dead animal tissue and as such are beneficial in nature as decomposer of dead animal carcasses. The appearance of these flies or maggots in the house typically indicates that an animal (i.e. rodent, bird, etc.) has died within the walls or in the attic. The larvae infest the animal carcass for 5-10 days before they leave the carcass and wander in search of a dry place to pupate. Maggots have hook-like mouthparts. Adults have sponge-like mouthparts similar to those of house flies. These maggots are unsavory but harmless.