Moth Flies

Moth fly resting on a white surface, viewed from above
Scientific Name
Members of subfamily Psychodinae
Psychodidae (moth flies, sand flies) in the order Diptera (flies)

Moth flies look like tiny, hairy moths. The fuzzy wings seem oversized, considering the tiny size of their bodies. Colors are dark, muted tan, gray, and black. A few species are mostly white. People usually notice them perching near sinks in the bathroom or kitchen. When disturbed, they usually don't fly very far away before landing again, for they are weak fliers, sometimes nearly hopping instead of flying.

Being true flies, and not moths, they have only one pair of wings. Unlike most other true flies, moth flies have rather long antennae, compared to their overall size, with 12 to 16 bulbous segments, each with a fringe of hairs. The wing veins are parallel, not netlike, on the outer two-thirds of the wings.

There are no other Missouri insects that look quite like these tiny, fuzzy, poor-flying creatures.

In North America north of Mexico, there are more than 100 species in the moth and sand fly family. Most of them are tropical or subtropical and do not occur in Missouri.

One common Missouri species is the filter fly, Clogmia albipunctata, which originally had a mostly tropical/Mediterranean distribution but now occurs throughout North America. The species name, albipunctata, means white-dotted, and this species has white dots around the margins of the wings, white on the leg segments, and whitish antennae. There are a pair of dark dots on each wing.

Larvae are rarely seen, due to their usual habitat inside drain pipes. They may be burped up into sinks, tubs, or basements if sewage pipes get backed up. They are not nearly as cute as the adults. They are segmented and wormlike, tapering on both ends, usually gray, tan, or brown. They lack eyes and legs. There is usually at least one dark, roughly rectangular spot on each segment on the back (dorsal side) of the animal. The last segment of the body has a breathing tube (which functions like a snorkel).

Similar species: In the same family as moth flies are the sand flies (subfamily Phlebotominae), which occur in tropical and subtropical areas. They look something like a cross between a moth fly and a mosquito, with longer legs and the habit of holding their wings up and off their bodies. They bite and drink the blood of humans and other vertebrates. They are infamous as vectors of tropical diseases, including the parasite that causes leishmaniasis, a disfiguring and frequently deadly disease that affects millions of people each year. This and other insect-borne tropical diseases are some of the many reasons to sleep under an insecticide-treated mosquito net if you ever go camping in the tropics.

Other Common Names
Drain Flies
Sewage Flies
Filth Flies
Bathroom Flies
Filter Flies

Adult size: less than ¼ inch. Larvae to about ⅜ inch.

Where To Find


Indoors, people usually notice adult moth flies perching next to sinks, tubs, or drains in the bathroom or kitchen, in public bathrooms, or perched on the walls in privies.

Outdoors, they may breed in clogged, wet gutters, air conditioners and cooling towers, potted plant trays, storm drains, soggy bird feeders, and other moist, shaded places where there is foul, organically rich water.

In natural habitats, they occur in wet, wooded areas, around seeps, near stagnant waters at the margins of wetlands, and so on. With their small size, drab coloration, and frozen posture, they are rarely noticed outdoors unless they land on an unnatural surface, such as the side of a building.

The larvae must develop in wet or very moist areas (see life cycle, below), so the adults, although they can potentially fly nearly anywhere, are found in those areas, too. Adults reportedly may be blown great distances by sustained winds.

Sewage treatment plants are another place where moth flies may be found in abundance.

These flies are also commonly attracted to lights at night.

Larvae live in and eat the organic material (algae, fungi, and bacteria) in the slimy, gelatinous layer of wet sludge that occurs on the inner surfaces of drain pipes of sinks and tubs, in sink traps, in outdoor garbage containers that stay wet, and in sewage pipes.

Adults sustain themselves with flower nectar and from drinking water.

Generally considered a nuisance in homes, but not necessarily unhealthful. They breed in unsanitary conditions, but they do not bite people and they are not strongly attracted to human foods. To control them, clean your drain pipes and traps with a brush to eliminate their habitat and food source. Make sure your plumbing isn't backing up. Consult a licensed exterminator for more information.

Life Cycle

Females fly into slime-coated, damp drainpipes or other suitable habitats and deposit masses containing dozens of eggs. Timing of hatching, development of larvae, and pupation varies with temperature and amount of nutrients available. The development from egg to adult emergence can take between a week and nearly a month. As adults, moth flies live for about two more weeks.

This small animal provides an interesting contrast in how we humans feel about insects. Most people probably consider the tiny, humble, fuzzy, mothlike adults (at least in small numbers) as rather cute, although not exactly welcome indoors. Meanwhile, the eyeless, grublike larvae, living amid sewage, slime, and filth, would strike most people as disgusting and unlovable.

The larvae, however, are important partners to humanity, because they play a large part in the wastewater-purification process at sewage treatment plants.

These humble insects help purify water, cleaning the environment and playing an important role in the decomposition process. They convert some pretty foul materials into a form (their own bodies) that is palatable to a wide range of insectivorous terrestrial animals, including spiders, birds, toads, frogs, reptiles, and many others.

In natural aquatic habitats, the eggs, larvae, and pupae become food for aquatic predators and scavengers, such as fish, crayfish, and many insects.

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About Land Invertebrates in Missouri
Invertebrates are animals without backbones, including earthworms, slugs, snails, and arthropods. Arthropods—invertebrates with “jointed legs” — are a group of invertebrates that includes crayfish, shrimp, millipedes, centipedes, mites, spiders, and insects. There may be as many as 10 million species of insects alive on earth today, and they probably constitute more than 90 percent all animal species.