Phorid flies are in the small category of flies, measuring up to 1/8 inch in length, including the wings. The most prominent feature of this fly is the humpbacked shape of its thorax. The most easily recognized feature (seen with the naked eye) is the habit of the adult Phorid fly running rapidly across surfaces instead of immediately flying when disturbed. Most flies immediately take flight.
Phorid flies develop by egg, larva, pupa and adult. The female will lay about 20 eggs at a time and will lay about 40 eggs in a 12 hour period. Each adult female phorid will lay approximately 500 eggs. The tiny eggs are deposited on or near the surface of decaying organic matter. Larvae emerge in 24 hours and feed for 8 to 16 days. The Phorid fly larvae then crawl to a drier spot to pupate. The life cycle from egg to adult can be completed in as little as 14 days (under ideal conditions) but may take as long as 37 days to complete their cycle.
Adult Phorid flies are fairly common in many habitats, but are most abundant about decaying plant and animal matter. When searching for Phorid fly breeding sources, remember that the larva can only survive in decaying organic matter that is moist. The first obvious place to check is where any fruits or vegetables or stored outside of refrigerators or coolers. Other areas to inspect would be recycling bins, seldom used (or cleaned) garbage cans, underneath and behind large appliances. Do not overlook drains where small flies are often found breeding in the super thin layer or film of debris that naturally accumulates in pipes, traps and drains. In commercial and residential structures, tiny amounts of organic debris are often found where the legs or feet of appliances, tables or cabinets touch the floor. These tiny spaces can harbor thousands of fly larvae. All small cracks and crevices at floor level need to be inspected and thoroughly cleaned.
The key is finding and eliminating all of the breeding sources. The insect light traps (eg : Insect Light Trap) are effective in harvesting adult flies and can be of particular value or as a temporary measure until the breeding source can be located and removed in commercial accounts.
Removal of drying of the organic matter where the larvae of phorid flies live will eliminate most problems. ULV application of non-residual pesticide (eg : Crackdown, Resigen) can also be used to kill the adults present.