Phorid flies also known as Humpback flies, also known as scuttle flies closely resemble fruit flies and can often be seen in the same areas that fruit flies would inhabit. Humpback flies are small flies generally around 1/8 inch. They can be identified by their escape habit of running rapidly across a surface rather than taking flight. They breed in and feed on moist decaying plant and organic matter, also frequenting unsanitary areas and can spread disease-causing bacteria onto exposed food products. 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, wall voids, or basements where plumbing leaks provide wet areas supporting mold or fungal growth. These breeding areas are occasionally very difficult to locate.
Other areas to check are where any fruits or vegetables are stored outside of refrigerators or coolers. Also inspect recycling bins, garbage cans, damp mop closets and used rag storage bins, and beneath refrigerators where dust and other organic deposits can be found in damp evaporation pans. When searching for breeding sources, remember that the larva can only survive in decaying organic matter that remains moist.