Blow Flies

(also known as Bottle Flies)


Adult blow flies, also frequently called bottle flies, are about the same size as the common house fly. They have one pair of wings, six legs and are often given a common name based upon their metallic colors of green, blue, black or copper. For example, those blow flies that have a metallic appearance are often referred to as green bottle flies, blue bottle flies, etc.


Females lay eggs primarily in decomposing organic matter such as grass clippings, garbage, dead animals, poorly managed compost piles and feces. The adult flies amass on the screens of windows and doors, which eventually allows the flies opportunity to overwinter inside.. It comes as no surprise that these flies are associated with a number of disease organisms that are found in human and animal filth.


Blow fly larvae feed upon organic matter where eggs are laid. Pupae do not feed. Adults feed on plant nectar they use as a source of carbohydrates.


Blow flies preferred habitat is the source of food on which the larvae feed. Some blow species show a tendency to feed upon a particular kind of organic matter. For example, the green blow fly is most likely to feed upon dog feces than are other blow fly species. As mentioned above, adults prefer to inhabit warm, protected sites when they go into their overwintering phase.


Blow flies develop via complete metamorphosis and have four developmental stages – egg, larva, pupa and adult. Their life cycle is fairly short – only about 2-4 weeks depending upon the blow fly species. Female adults lay eggs on garbage or some other chosen developmental source in clusters of about 140-200 eggs. Under favorable conditions, blow fly eggs hatch in as little as one day and become larvae. Larvae feed for about 1-2 weeks, crawl to a dark, secluded place where the larvae become pupae. After about a week in the pupal stage, adults are formed.


Visual evidence of the adults and the feeding larvae are the most obvious signs of a blow fly infestation. One of the more interesting, if not disgusting, things to see is an actively feeding swarm of blow fly maggots (larvae) consuming a dead animal or piles of feces. In addition, an infestation in the attic or basement may be noticed by the accumulation of blow fly adults in light fixtures or around windows.


Keeping trash cans clean and removing suitable sources of larval food are the most effective methods of prevention. Also, there are some effective fly traps that may be used to capture blow flies, but these traps are not effective in preventing flies over a large area. As with most other flying insects, exclusion via keeping trash receptacles tightly closed, windows and doors closed and openings inside a home well sealed and screened are also important.


If prevention is not sufficient, other methods of control, like using insecticide baits, liquids or aerosols to kill feeding larvae are useful. In addition, using insecticide products to treat surfaces where adults are seen resting may also be effective. However, one should never forget about a sturdy fly swatter to help with small scale fly control.