A source for information on flies
Phorid Fly Phoridae spp.
Phorid flies are
yellowish-brown with a small head and large black eyes. They have veined wings and an arched thorax, earning them
the nickname “humpbacked fly”. They resemble Fruit flies in appearance, but they lack their prominent red eye
Phorid flies are minute, and are
usually 1/16-1/8-inch long.
Phorid flies reproduce in moist areas where food and water are present. Eggs are often laid directly on decaying
material, and hatch within 24 hours. Their entire life cycle lasts about 25 days or more, depending on temperature,
food, and moisture available. Females are very attracted to odors of decaying animal remains and readily lay eggs
on or near it.
However, larvae do not initiate wounds or attack healthy animals or humans. Adults have sponging mouthparts and
are often confused with fruit flies and fungus gnats due to their small size, breeding habits, and flight pattern.
Phorid flies may run rapidly across windows, TV screens, tables, and walls in short, jerky movements, appearing
reluctant to fly.
Phorid flies can breed in more types of materials than any other structure-infesting fly. They can become a
nuisance in hospitals, food establishments, or homes. They can also be found outdoors in decaying organic matter
such as vegetation, animal feces, carcasses of animals, decaying insects and nests of ants, termites, bees and
wasps. In nature, they are typically associated with dead animals and heavily decaying vegetation. In
mausoleums, they are known as “coffin flies” because they breed inside bodies stored in the crypts and coffins. In
buildings, they may found breeding in drains, trash containers, dumpsters, rotting produce, recycle bins, grease
traps, garbage disposals, crawlspaces, and any site where moist organic matter can accumulate for five days or
longer. Phorid flies have also been found to breed in poorly stored meats, damaged containers of moist foods, and
organic-based glues and paints.
Larvae have also been found feeding in sour milk, decaying plants, open animal and human wounds, decaying animal
and human (cadaver) flesh, feces, laboratory culture media, clogged drains, mausoleum crypts, human tissue at
hospitals, plant soil, garbage cans and disposals, etc.
The Phorid fly has been utilized as a biological control agent in the eradication of fire ants. They “parasitize”
fire ants by depositing eggs that hatch into larvae and pupate inside the fire ant’s head capsule.
Adult flies use chemical cues to locate fire ants, which they attack and lay an egg in the ant’s thorax. The
maggot hatching from the egg then migrates to the ant’s head. As the fly pupates, it releases enzymes that cause
the head to fall off, killing the ant.
Since Phorid flies originate in filthy conditions, there is a possibility of transmitting certain diseases. This is
of particular concern since they often turn up in burn units, operating rooms and pathology labs where sterility is
of extreme importance. It is important to locate and eliminate the larval breeding source; concentrations of adult
flies and decaying odors are good indicators of nearby breeding grounds.
The Phorid fly Larvae develop in moist areas where
organic material and standing water are present. Phorid larvae also develop in animal matter. The entire life cycle
lasts 25 days or more, depending on the environmental conditions and the availability of food.
Though electrocuting devices and sticky traps help minimize Phorid fly populations, other steps are necessary in
order to eradicate them. Start by eliminating or reducing moisture sources and avoid accumulation of wet organic
matter in and around structures, as they are preferred breeding grounds. Seal cracks and crevices to prevent entry,
and dispose of garbage and old bird and insect nests. The key to controlling phorid flies is finding the breeding
sites and removing them by proper cleaning practices. Phorid flies, like other types of small flies, can be
difficult to totally eliminate because they can breed in such small amounts of organic matter. A number of breeding
sites can be found and eliminated while others may easily be overlooked. The inspection needs to focus on finding
all sites where moist organic matter has accumulated and then removing that matter completely.
On occasion, drain line breaks under slabs or in crawlspaces
can result in huge phorid fly populations in homes, restaurants, or other buildings. Drain breaks beneath a slab
floor will require the expertise of a plumber to diagnose. If flies are found to be breeding under the slab, the
slab will need to be broken open and the drain line repaired. If the wet, contaminated soil is not removed and
replaced with fresh, dry soil, the phorid fly problem will persist.
Indoors, thoroughly clean drain pipes and traps with a stiff-bristled brush. It even helps to remove the trap and
use a “snake” in clogged rains to clean pipes of all buildup, which can serve as a food source for larvae. Bleach
may be poured into the pipes after a thorough cleaning, followed by a careful flushing with boiling