The phorids, also known as humpbacked flies, are small to minute flies that resemble fruit flies in appearance. The Phorid fly lacks the red eye color that is the classic trademark of the fruit fly. 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 severe arch of the thorax gives it the common nickname of humpbacked fly. 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 Fly Life History

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.

Inspecting for Phorid Flies

Adult Phorid flies are fairly common in many habitats, but are most abundant about decaying plant and animal matter. In structures, these flies can be found breeding wherever moisture exists around plumbing and drains in bathroom and kitchen areas, garbage containers, garbage disposals, crawl space areas and basements. These breeding areas are occasionally very difficult to locate. Although it is primarily used to reduce fly populations, a Gold Stick pheromone trap can be used to monitor different areas of the home. This will help identify the areas populated with flies and help locate their possible breeding sites.

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.

Once one source has been located, continue with your inspection. Phorid flies easily follow air currents and usually have several breeding places in any structure. Do not assume that all of your breeding sources are indoors; fruit flies will wander in from nearby dumpsters, outdoor garbage cans or even damp compost piles where fruits and vegetables are disposed.