Flies in the home

Order: Diptera

Description

Adult flies are winged and the most frequently observed life stage. Larvae are pale, legless maggots that often migrate away from their food source to pupate. The pupae are typically tan or brown.
There are various fly species that can occur in homes. Those that can reproduce indoors include Drosophila spp., certain Orfelia spp. and Bradysia spp., and some species of phorid and psychodid flies, which collectively reproduce on overripe fruit, in the soil of houseplants, and within drains, respectively. These pests are a nuisance but do not pose a threat to human health. However, some species such as the house fly (Musca domestica) can develop in garbage or other decomposing material and may spread disease-causing microorganisms via physical contact with food or food preparation areas.

Sanitation is an important first step in managing most types of flies in the home. Locating and eliminating potential breeding sources will prevent flies from reproducing, although adults may remain for over a week until they die out. The type of breeding source depends on the fly of concern.

Phormia regina, Calliphora spp., and Pollenia spp.
In Colorado, common species include the black blow fly (Phormia regina), some Calliphora spp., and some Pollenia spp. The black blow fly and Calliphora spp. seek winter shelter in the fall and are large and metallic gray, blue, or black. They are attracted to gas leaks and decomposing animals that have recently died.

The Pollenia spp. are dark gray and easily distinguished by the presence of golden hairs on top of the thorax. These flies are earthworm parasites that can become abundant in lawns. In late summer and early autumn, the adults enter a semi-dormant state and can be seen on sun-exposed sides of buildings. They are most likely to be found in upper floors of buildings as they tend to migrate upward when seeking shelter.

Flies that breed on moist garbage include blow flies, house flies, and little house flies. These pests can breed rapidly at warmer temperatures. Covering garbage containers and regularly removing garbage to covered outdoor containers will reduce the availability of breeding sites. Removing garbage every four to five days may be necessary during summer.

House fly 
Although the house fly (Musca domestica) is very well known among the house-infesting flies, it is not the most common species inhabiting homes in Colorado. These flies are about 6.4 mm (1/4 inch) long and typically have gray bodies with broad dark stripes on the thorax. Some have yellow coloration along the sides. Larvae can develop in garbage, animal waste, animal feed, and culled produce. Due to its feeding and breeding habits, the house fly poses a risk to human health, especially when they contact food or surfaces where food is prepared.

Little house fly 
As the name suggests, the little house fly (Fannia canicularis) resembles the house fly but is smaller and has several distinct yellow segments at the rear of its body. Adults are about 4.8 mm (3/16 inches) long. Eggs are laid and larvae feed on decaying animal matter or manure with high moisture. This species is associated with structures used for housing poultry and livestock.

Ceroxys latiusculus
This species is the same size as a house fly but has dark band patterns on the wings. In some locations, these flies invade homes in early autumn and can be found around windows. They do not survive indoors and will usually die indoors by the end of November. Larvae develop in the stems of several native plants in the family Asteraceae.

Orfelia spp. and Bradysia spp.
Fly species in both genera are about 3 mm long, dark, and resemble mosquitoes. They do not bite and are most frequently observed aggregating around windows in the fall and winter. The soil of houseplants can serve as a breeding site. While they are considered a nuisance, they do not typically damage plants.

The soil of houseplants should be allowed to dry between waterings, and decomposing plant materials should be discarded to prevent infestations of Orfelia spp. and Bradysia spp. Once established, there are insecticides available for controlling infestations, which include certain formulations of Bacillus thuringiensis var. israelensis that are often sold at nurseries or garden centers.

Crane flies 
Crane flies (Family: Tepulidae) are large flies that have wingspans ranging from 5-85 mm (1/5-3 ¼ inches), depending on the species. These flies are in the family Tipulidae, which includes over 15,000 species worldwide. These insects are abundant in areas with high levels of moisture and organic matter, such as waterways and ponds. While they may resemble large mosquitoes, crane flies do not bite. However, crane fly larvae can be pests of turfgrass.

Drosophila spp.
At 2-2.5 mm long, Drosophila spp. are some of the smallest flies found indoors. Many species have bright red eyes and are usually light brown. Their larvae develop on overripe fruit or other fermenting sources of yeast such as the residue in an unwashed beer can. Populations are greatest in the late summer and early fall when infested fruits are moved indoors during the harvest season.

In homes with infestations of Drosophila spp., it is recommended to consume, cover, or refrigerate all ripe and overripe fruit until the adults have died out. Any discarded produce should be placed outdoors and thoroughly wash any food residues that collect on waste containers. Beverage containers should also be thoroughly rinsed before discarding.

Phorid and psychodid flies
This group includes two different families that reproduce in drains, Phoridae and Psychodidae. The phorid flies are about 3 mm long and resemble Drosophila spp, but with a distinct large hump on the thorax that is visible when viewed from the side. When indoors, they often breed in food waste in drains.

The psychodid flies are 2 mm long, gray, and their wings have distinct small scales, which makes the flies superficially resemble small moths. The larvae develop by feeding on bacterial layers within plumbing that is continuously wet. Other potential breeding sites include moistened filters of swamp coolers and fish tanks. When large numbers of these flies are present, this usually indicates a break or leak in drainpipes. Removing bacterial gel coats and food waste lodged in plumbing will reduce the availability of breeding sites for phorid and psychodid flies. Pipes can be cleaned mechanically with a brush or chemically with drain cleaners. Drain cleaners consisting of foam formulations that contain enzymes are effective at breaking down food residues in plumbing.