This particular fly is fairly easy to identify. They are 1/16 to 3/16” long, usually grey to back and fuzzy in appearance. The most distinct characteristic is the ‘inverted valentine heart’ shape when they are at rest. These flies breed in moist, decaying organic material. As they are weak fliers, their presence is indicative of a nearby breeding source.
Breeding sources can include: organic slime build-up in drains, garbage cans, air conditioners, compost bins and septic tanks. Since they normally inhabit sewers, finding them could indicate something as simple as a drain trap that has been allowed to dry up from non-use (run water in ALL drains at least every 2 weeks) to a broken sewer line beneath a basement floor. Control requires locating the breeding source.
These flies are often described as ‘gnats’ of ‘fruit flies’ as they of similar size. The ‘humpback’ name comes from their appearance when viewed from the side. Indoors they can often be seen at windows where they tend to ’run’ as much as fly. In Chester County, large swarms of these flies can be seen outside on a summer evening and can often enter structures through window screens.
Breeding sources include those of the Moth Fly but can also include animal waste, overwatered potted plants, corpses or virtually any moist organic material.