When people see small-sized flies in their home, their first thought is that they must be fruit flies. However, there are a handful of other kinds of small flies that may also be found in homes. One common type is the phorid (FOUR-id) fly also know as humpbacked fly, coffin fly, and scuttle fly.
This fly is about 1/8 inch long, tannish to dark brown and has a hump-shaped thorax. Under magnification, you can see the characteristic pattern of veins in their wings comprised of two strong veins at the top of the wings with three or four parallel veins radiating out from there.
Fruit flies and phorid look similar and can be easily confused. The easiest way to distinguish between them is the eyes. While fruit flies usually have red eyes, phorid flies lack this and have dark colored eyes. Phorid flies also move characteristically in a rapid, jerky motion. Although they can fly, they often prefer to walk or run on counters, walls and other surfaces. Fruit flies (as well as other small sized flies) more commonly fly.
Phorid flies are found in many types of moist decaying organic material. They can be found in drains, especially in bathroom sinks and showers, food residues in trash containers, rotting food, infrequently used garbage disposals, dirty mops and old dish rags, potting soil, organic material on the bottom of pet cages, and sewage from broken sewer lines. They are also common in schools and other buildings with a food service area in the cracks of kitchen equipment or underneath them. They have even been know to infest mausoleums and feed on human corpses!
These flies can occur in large numbers and become a significant nuisance. Phorid flies can potentially be a mechanical vector of disease organisms because they visit rotting foods and generally unclean areas. Although this can happen, they are generally not considered to be a medical problem.
The most effective control of phorid flies to locate and remove the moist organic material that the larvae develop in. However, finding the food source may be easier said than done and often requires detective work to locate the infestation. Remember that this could be found in a variety of different places. Be flexible in your thinking as the problem could occur in unexpected sites. The keys are moist, organic material.
Despite this work it takes to find the source, it is worth the extra effort and will result in a long-term solution to the problem. It may be tempting to spray the adult flies with an insecticide to control the problem. However, as long as there is a food source, the phorid flies will continue to occur.
Originally published in Yard & Garden Line News, Volume 5, Number 18, December 1, 2003