The trickling filter fly, better known as the drain fly, is a tiny, fuzzy-winged fly that turns up on bathroom and kitchen walls near sinks and showers. Its name comes from sewage treatment plants, where its larvae live in the slimy film on the filter beds and help break down waste. It is native to North America and has spread around the world.
Appearance
- Appearance
- Adults are gray and mottled, about 1/12–1/6 in (2–4 mm) long, with females larger than males. Broad wings are covered with dense, hairlike scales along the veins. Larvae are slender and white to pale brown, with a breathing tube at the rear end.
Look-alikes
Bathroom moth flyClogmia albipunctata
This relative is larger, about 3/16 in (4–5 mm), covered in gray-black hairs, with white spots of hair near the wing tips. The trickling filter fly is smaller and has small dark spots at the wing tips.
Why they get mixed upBoth are fuzzy moth flies that breed in household drains.
Where it lives
- Typical habitats
- Household drains
- Sewage treatment plants
- Wet soil
- Range
- Native to North America and now found worldwide, including Europe, western Asia, and South America.
- Preferred conditions
- Larvae need wet places rich in organic matter: the gelatinous film inside drains and overflow pipes, trickling filters at sewage plants, ditches, and the top inch or so of wet soil.
Behavior
- Diet
- Larvae feed on the film of wet, decaying organic matter in drains and filter beds, along with the microbes living in it.
- Activity
- Adults are weak fliers that mostly run, hop, or make short flights, and rarely move far from where they developed. Outdoors in temperate areas, they start emerging in spring and peak in late summer.
Life cycle
- Reproduction
- Females lay up to 100 eggs on wet surfaces, usually in jelly-like masses of 15 to 40. Eggs hatch in less than two days at about 70°F (21°C).
- Larva
- The larval stage is the longest, about 9–15 days at 70°F (21°C) and about 8 days at 85°F (29.5°C). Pupae last 1–2 days, and the whole life cycle usually takes 21–27 days.
- Lifespan
- Adult males live only a few days; unmated females live up to about a week.
Cautions
- Cautions
- Drain flies don't bite and are not known to transmit disease. Very large infestations can cause breathing problems when people inhale the fine scales they shed. To get rid of them, scrub the organic buildup out of the drain with a pipe brush and dry out any standing water; taping over a drain overnight shows whether flies are coming from it.
Conservation
- IUCN Red List
- NENot EvaluatedNot yet assessed
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