Phorid flies (Diptera: Phoridae) have several common names, including scuttle flies, sewer flies, and humpback flies.
Adult phorid flies are small flies generally under 5 mm (0.2 inch) in length. Frequently found in homes and buildings, they are often mistaken for fruit flies. Unlike fruit flies, phorid flies characteristically run short distances before briefly pausing and then abruptly running in a different direction. They often run away instead of flying away.
Adult phorid flies are typically colored shades of brown or tan; some have dark bands across the abdomen (Fig. 1). Their wings are usually clear with several strong, dark veins crowded towards the base of the wing. Phorid flies have a typical “humped back” appearance with a small head placed somewhat lower than the front of the strongly arched thorax (Fig. 2). The head may be bristly and the legs are noticeably long.
Phorid flies have a complete life cycle consisting of an egg, larval, pupal, and adult stages. The immature egg, larval, and pupal stages are small and rarely noticed by homeowners. Phorid flies reproduce in moist, decaying plant and animal matter. If phorid flies are breeding indoors, the immature stages will likely be associated with dirty garbage cans, clogged drains, or similar locations. Multiple generations of phorid flies occur each year, limited primarily by cold temperatures and the availability of suitable food sources.
Like other members of the group of flies collectively known as “filth flies,” adult phorid flies feed on liquids from decaying organic material, including rotting garbage, compost piles, carrion, and dung. They may transfer disease organisms to fresh foods intended for human consumption if they have access to them. Adult phorid flies do not bite humans or animals. The vast majority of phorid fly species live outdoors in a wide array of habitats with little or no impact on humans. Some species are parasitoids of ants and have been studied as potential control agents of fire ants (Solenopsis spp.). Other species develop in fungi and can be pests of mushroom farms.
Habitat and Distribution
Cosmopolitan; phorid flies can be found in association with human habitation as well as in the wild.
Sanitation is extremely important in controlling phorid flies. Garbage cans and recycling bins should be emptied and cleaned on a regular basis so that food and liquid don’t accumulate and support fly populations in them. Scrub tiles, small ledges under appliances, or any cracks where organic material can accumulate and support phorid fly populations. Drip or condensation pans under refrigerators, air conditioners, and dehumidifiers should be kept clean to prevent breeding by phorid and other nuisance flies. Check around dishwashers, refrigerators, washing machines, and under sinks for any leaks, pooled water, or even damp rags or sponges.
Keep sink, tub, and floor drains clean so organic matter does not build up in them. Apply tape sticky side down over drain openings to determine if phorid flies are emerging from drain lines. Occasionally sewer lines or drainage pipes break and release decaying organic material into the soil or under foundations or concrete slabs. Large numbers of phorid flies can breed in the soil contaminated by the leaking pipe. A plumber should be consulted in these circumstances.
Use a fly swatter or an aerosol spray to kill adult flies when present. Do not contaminate foods or eating utensils with insecticides. Sticky fly tape, glue traps, or lighted insect trap lights may reduce adult populations, but sanitation and eliminating the breeding source is key to controlling phorid larvae.
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March 1, 2021