Many of us are familiar with fruit flies and the aggravation they can cause when they infest material and breed in our homes and offices. There is another small family of flies, the humpbacked or coffin flies, often confused with fruit flies. These small flies vary in their life histories, ranging from infesting decaying plant or animal matter, fungi, dead insects under the refrigerator, sludge in the bottom of trash cans, liquids remaining in bottle and cans in recycling bins, and in drains and septic tanks to a beneficial life history as a biological control agent of the red imported fire ant, termites and other insects.
They can be the bane of the mausoleum industry, because the female lays her eggs at the cracks and crevices of “sealed” coffins, and the larvae are good at getting in and feeding, hence the name, coffin flies. They can also be a serious problem in hospitals and restaurants where sanitation is critical.
These little flies can be identified by looking at the hind leg. The first segment of the hind leg, the femora, is laterally flattened (leg is not rounded but wide and flat, see pictures). This is the simplest characteristic for identification and can be observed with a magnifying glass. Other features used include the humpbacked appearance and the wing venation. There are 350 species in the United States.
Phorid flies have complete metamorphosis, developing from egg, larva, pupa, to adult. A female is capable of laying 20 eggs at a time and about 500 in her lifetime. Eggs are laid near suitable host material and larvae hatch in 24 hours. The larvae feed for 8 to 16 days and then crawl to a drier spot to pupate. The life cycle can be completed in 14 days under ideal conditions, but it can take a long as 37 days.
Where problems exist, sanitation is the best management tool. These little flies can develop in the smallest of locations. Food collected under a table leg or the leg of a refrigerator or a crack or crevice where food crumbs and moisture can accumulate can be a source for the development for hundreds of larvae. Remove decaying materials and clean out drains, making sure there are no leaks or breaks in sewer or drain lines. Move appliances and furniture and clean them to assure removal of potential habitats and food. The adult flies can be controlled with a spray application of pyrethroids you can purchase over the counter or at the local grocery.
Place your trash cans away from the house or doorway, and keep them tightly closed. Wash them out periodically to remove potential sources for breeding.