Fly Identification

- House flies, mosquitoes, crane flies, & gnats -

Summary: The flies (Diptera) are an extremely large and diverse group of insects including mosquitoes, gnats, crane flies, house flies, and even horse and deer flies. Almost all flies require water to develop and the habitat often determines what type of flies are common.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

There are many thousands of species of flies (Diptera) worldwide including some of the most important insects in terms of their direct impacts on our health and property. The flies include mosquitoes, and other small delicate gnat-like insects, larger crane flies, as well as house flies and even large horse and deer flies. They all belong to the insect order called Diptera and are distinguished from all other insects by having only 1 pair of wings as adults, other winged insects usually have two pairs of wings.

Researchers recognize two broad groups of flies, "higher flies" and "primitive flies". The so-called higher flies include, for example, house flies, horse flies, cluster flies, fruit flies and black flies while the primitive flies are the mosquitoes, crane flies, midges, gnats, and other small, delicate flies.

house fly
house fly about 1/4" long

Fly larvae (maggots)

Fly larvae are also called maggots. Depending on the fly, maggots can develop in water, wet soil, manure, rotting vegetable matter, decomposing animal tissue, and, in some cases, living animal and plant tissue, some are even predators. Maggots are generally legless and without a distinct "head" but some primitive flies, for example fungus gnats, have a distinct, dark head capsule.

Flies undergo complete metamorphosis. This means that in addition to the larval stage flies exhibit a pupal stage in which the transformation from larva to adult occurs. Fly pupae are distinctive between groups and can often aid in identification and are often used as the target in fly control programs.

Fly control

Effective fly control depends on determining the identity of the pest fly because this will often be a good clue about where the flies are developing. The site where fly larvae develop is sometimes called the "breeding source" and once this source is found, you can often reduce fly numbers simply by managing, treating or eliminating the source. Sometimes the source is obvious such as a mosquito-infested pond or a garbage dumpster but sometimes it is not, for example a poorly drained field can be the source of a tiny fly called a biting midge. See the links in the table below for control information about particular pest flies.

Sources of pest flies

Most fly larvae, or maggots, need very wet conditions and some are even aquatic. Use the table below to identify different habitats where common pest species can develop and the links for specific information and pictures about each pest.

Where Do Flies Come From?

Where Larvae Live
Flies You Might Find
Pest Type
Standing water such as a birdbath or lake mosquitoes biting

Fast flowing water of a creek or river black flies biting

Internal earthworm parasite cluster fly household nuisance

Organic "gunk" in a household drains drain flies household nuisance

Wet, poorly drained pasture biting midges biting

Damp soil at edge of a pond horse and deer flies biting

Damp, organically rich soil fungus gnats household nuisance

Fresh manure house flies, stable flies biting

Rotting fruit or vegetable matter vinegar flies (aka "fruit flies") household nuisance

Fresh fruit on a tree fruit flies agricultural

Well-watered home lawn or athletic field crane flies landscape
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