Drain fly

Drain flies are small, fuzzy flies in the family Psychodidae, often called moth flies, sink flies, or sewer flies.

Drain flies are small, fuzzy flies in the family Psychodidae, often called moth flies, sink flies, or sewer flies. They are associated with moist, organic buildup in drains, sewage systems, and other damp places, where their larvae feed on decaying material and microbial slime. Adult drain flies are generally non-biting and are considered a household nuisance; they are a common pest in Canadian homes, though they are relatively harmless compared with other flies.

Identification

Drain flies are small, about 1/16 to 1/4 inch long. Their bodies and wings are covered with hairs, giving them a moth-like appearance. They are often mistaken for fruit flies or fungus gnats. They are usually noticed resting on walls, sinks, or bathroom surfaces near drains.

Life cycle and habitat

Female drain flies lay eggs in moist organic material. The larvae feed on slime, bacteria, algae, and decomposing matter in drains and similar wet environments. Development is fast in warm, wet conditions, which is why infestations can increase quickly in homes and buildings. Some species commonly encountered indoors include Clogmia albipunctata.

Behaviour and human impact

Drain flies are not known to bite humans and are generally harmless to structures. They are mainly a nuisance pest. Large infestations are most often linked to untreated drains, leaks, sewage backups, or other hidden wet breeding sites.

Control and prevention

Effective control depends on eliminating the breeding source rather than spraying adult flies. Recommended measures include cleaning drains, removing organic buildup, fixing leaks, emptying standing water, and cleaning nearby drains or sewage-related areas. Insecticides alone are usually not effective in drains.