The blow fly is known for the habit of its larvae, or immature flies, infesting animal carcasses. They are found all over the world, where ever there are people, you will find them.
They are slightly larger than true houseflies, and the bodies of many are metallic blue or green in colour. Worldwide, there are about 1200 species of blow flies, and in North America, there are 80.
In many areas such as the Pacific Northwest, they are the most common type of flies found in human habitations. Blow flies have a length of up to 16 mm, they have robust bodies and wide heads.
The name blow fly comes from the bloated condition of the rotting animal carcasses that their larvae, known as maggots, infest. The most frequent species found under these conditions is the common blowfly. The adult blow flies, on the other hand, feed primarily on flower nectar, plant sap, and other sugary materials.
The female typically lays her eggs on the body of a recently killed animal. The eggs hatch quickly into maggots and then feed on the decaying tissues. In warm weather, some species can complete their larval growth within a week. They then burrow into the soil and pupate, to emerge later as adult flies.
Blow flies play an essential role in nature by decomposing dead animal tissue. The cluster fly species of blow fly is an exception: its larvae prey only on worms.
Blow fly maggots are important in forensic analyses in cases of homicide and other human deaths. Because maggots grow at constant rates, their size and stage of development can provide clues to the time and conditions of death. Blow flies have played a role in medicine: species such as the green bottle fly and the black blow fly are sometimes used to clean open wounds in humans because the maggots tend to feed only on decayed tissue, like that caused by gangrene and the wounds of burn victims.