When you find your home overrun with very small, almost microscopic flies that are much smaller than the familiar houseflies, there are three possible culprits: fruit flies, drain flies, or phorid flies. Identification can be difficult given the small size of the creatures, but phorid flies have several distinguishing features:
- When inspected closely, the back of a phorid fly will appear to have a humped shape.
- Phorid flies tend to fly and walk in an erratic pattern, rather than in a predictable straight line.
- Phorid flies are often seen walking along a surface, rather than flying. Unlike most flies, which take flight when escaping, phorid flies may attempt to run away.
- Phorid flies often appear around dead animals, such as rodents.
While at a casual glance, phorid flies can be mistaken for fruit flies and drain flies, close inspection will reveal that they don't have the red eyes found in fruit flies, nor are they attracted to vinegar—one of the key identifying traits of fruit flies. Nor do phorid flies have the fuzzy, moth-like bodies found on drain flies. And drain flies, since they prefer damp, dark locations, are almost always found near sink or floor drains—not usually the preferred location for phorid flies.
Biology and Lifecycle of the Phorid Fly
Phorid flies include about 4,000 species of tiny flies within the Phoridae family. Usually about 1/8 inch long, phorid flies typically have a hump on the back and are most notably identified by the habit of running away on surfaces rather than flying—a behavior that is responsible for the other common name for this insect—the scuttle fly.
Other precise identifying features are nearly impossible to spot by eye, given the fly's minuscule size, but these insects are notorious for feeding on decaying organic material, especially the corpses of animals. If small swarms of tiny flies appear at the same time as the suspicious odor of a decaying rodent, it is very likely you are seeing phorid flies. This fly has also been known as the coffin fly because in years past it was sometimes seen in human coffins.
Egg-to-adult reproduction for the phorid fly occurs in about 25 days or less. The cycle begins with adult flies laying eggs in decaying organic material. In about 24 hours, the larvae emerge, then feed and grow for eight to 16 days before finding a dry spot in which to pupate. Within a few days, the pupae mature and emerge into adult insects. Phorid flies reproduce very quickly and will remain until the decaying material that provides them food and a breeding location are completely consumed.
5 Ways to Get Rid of Phorid Flies
Find and Eliminate Decaying Matter
The very best solution for a phorid fly infestation is to locate and eliminate whatever decaying organic material being used by the flies to feed and breed. This is often the only method required to get rid of phorid flies, since once the feeding/breeding material is eliminated, these short-lived insects quickly vanish. But you can expect to have ongoing difficulties with phorid flies in areas where decaying organic material is common, such as around garbage cans or sewer floor drains.
However, if the flies have not disappeared within a week after removal, it is likely that you have not yet found and eliminated the organic feeding/breeding source.
Kill Adult Flies With Safe Pesticide
Adult flies can be combatted with a contact spray containing pyrethrins. These pesticides use a natural compound derived from chrysanthemum flowers and will not harm pets or humans. This substance is, however, toxic to fish, so it should not be used where runoff into rivers, lakes, and streams is possible.
Pyrethrin is a contact killer only—the flies need to be hit with a direct spray. It doesn't do much to repel flies.
Use an Electronic Bug Zapper
Bug lights ("zappers") will also attract and kill adult phorid flies, along with other insects. These zappers can be somewhat annoying, however, as they cause insects to congregate wherever the appliance is positioned.
Use Sticky Traps
Sticky pads or strips can be a useful method for trapping all manner of flies in areas where they habitually congregate, such as around garbage containers. These products are coated with a sticky, waxy material and sweet-smelling bait; they hold the insects tight as soon as they alight.
Use Essential Oil Spray
A variety of organic pesticides made from a blend of essential oils from citrus plants and various herbs can be effective as a contact spray and repellant for phorid flies and other insects. These insecticides are sold under a variety of brands, such as Wondercide.
You can also make your own essential oil pesticide by combining a few drops each of eucalyptus, peppermint, lavender, and lemongrass oils in a spray bottle mixed with water and a small amount of dish soap.
What Causes Phorid Flies?
Phorid flies can feed and breed in any organic matter, but they often prefer dead animal tissues. Where phorid flies are seen, there is a very good chance of finding a dead, decaying rodent, bird, or bat hidden somewhere in the walls or floors. Phorid flies are often the first pest drawn to these corpses, followed by other scavenger insects, such as carpet beetles, mites, and other flies. It is wise to begin looking at the first appearance of phorid flies before the corpse starts to smell.
Phorid flies can also be found in other areas where decaying, rotting material is found, such as garbage cans and even diaper pails that aren't regularly emptied and cleaned.
Phorid flies also feed on fungi, and are thus often found in the vicinity of mushrooms, toadstools, mildew, or other fungi. The organic material that collects in drain traps and branch drains is also a prime location for phorid flies.
How to Prevent Phorid Flies
If you have phorid flies coming up from drains, have your sewer system inspected for breaks. Flush floor drains and fixture drains frequently and copiously to eliminate organic material. Keep garbage disposals clean, as well. Bleach flushed through drains will kill fly larvae.
Make sure to keep kitchens and bathrooms spotless, especially floor areas around the bottoms of appliances and fixtures. Clean up fastidiously after pets.
Always keep an eye out for dead animals, such as mice and other insects. If you are trapping or baiting rodents, make sure any corpses are removed immediately.
Do Phorid Flies Carry or Spread Diseases?
Phorid flies commonly feed on dead, decaying organic material. Because they frequent unsanitary places, including drain pipes, they have the potential for transmitting various bacteria that cause illness. But these insects are not as mobile as houseflies, and thus don't pose quite the same risk for spreading serious diseases, such as salmonellosis, cholera, and typhoid. Still, where phorid flies are present, you can be assured that decaying organic material and the associated dangerous bacteria are present.
Do Phorid Flies Bite?
Phorid flies are too small to effectively bite humans and they can't transmit pathogens in this way. The health risk comes from the flies transferring bacteria and other pathogens from decaying material to other surfaces via their feet and bodies.
How Long Do Phorid Flies Live?
The entire lifecycle of the phorid fly is usually contained within no more than 25 days, but the adult flies themselves live for only live a few days. The rest of the lifecycle is occupied by the juvenile phases—egg, larva, and pupa. If the source of decay is removed, the phorid fly infestation will disappear very quickly.
Do Chemical Pesticides Work for Phorid Flies?
A variety of chemical contact pesticides will kill phorid flies, though permanent elimination is possible only if the decaying material that fosters their breeding is also eliminated. Because the lifecycle of the phorid fly is so short, it's generally easier and safer just to remove the decaying material upon which they feed and breed. Denied this rotting material, the infestation vanishes almost immediately. Even professional exterminators try to avoid chemicals when it comes to phorid flies.
Do Phorid Fies Have an Ecological Function?
All animal species serve a function within the larger ecology of their environment, and in the case of phorid flies, this function is to consume dead, decaying organic material. In an outdoor location, phorid flies and other carrion-consuming species serve to "clean up" the environment. Without such insects, animal corpses and their associated pathogens would be present for much longer. This very necessary function becomes a problem in homes simply because phorid flies have the potential for transferring pathogens.
When Do I Need an Exterminator?
In rare instances, the source of an infestation can be maddeningly hard to find, and in these cases it's possible that the flies are breeding in earthen spaces beneath a concrete slab. A professional exterminator may be the best choice here. The technician will likely lift up the flooring or bore holes to apply a serious pesticide to take care of the problem.
When combatting mice or rats, the use of rodent bait poisons should be avoided, since this often causes rats and mice to die inside walls or below floors, where the decaying corpses create a haven for phorid flies. When rodents are a problem, use traps so the rodents can be removed from the home.