Penn State Extension


Moth Flies in the Home

An annoying and troublesome pest that concerns numerous homeowners is the moth fly, also commonly known as the drain fly, filter fly, or sewage fly. Moth flies are frequently found indoors on windows, sinks and walls. The source of the fly infestation is generally from sinks and floor drains, or from nearby sewage plants or waste disposal areas. Polluted waters and wet organic materials are preferred breeding areas of the fly.

The adult fly (Fig. 1) is about one-tenth inch long (about one-third the size of a housefly). It has a dark gray body and lighter colored wings. The body and wings are densely covered with long hairs which give the body a fuzzy or hairy appearance, hence the name “moth fly”.

Eggs are deposited throughout the spring and summer in moist, decomposing organic materials. The gelatinous organic deposits, which accumulate in drains, provide an ideal breeding site. Eggs hatch into the maggots (Fig. 2), which feed in this organic matter. Under favorable conditions, maggots mature in about two weeks and form a hard shell (puparium) within which the pupa forms and from which the adult fly emerges.

Figure 1. Moth fly adult

Moth fly larvae

Figure 2. Moth fly larvae


Control varies with the origin of the moth fly infestation. The most economical and sanitary way is to remove the organic material in which they breed. This requires cleaning sinks, drain pipes, and traps with a stiff wire brush or by steam. Several new products are now available that contain either bacteria or enzymes which breakdown the gelatinous scum in drains. They are applied as either a pour around the drain lip or injected as foam. Most pest management companies provide this as a service. To determine which drain is infested, place a jar over the outlet or tape a plastic bag over the opening of the overflow outlet. Check the container at intervals for adult flies.


Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

Authored by: Steve Jacobs, Sr. Extension Associate

Reviewed January 2014

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