Adults: 3–4 days (University of Kentucky); unmated females up to 7 (UF/IFAS). Egg to adult: about 11–19 days at about 21 °C (UF/IFAS); the whole life cycle about 10–15 days at 70 °F (University of Kentucky ENTFACT-615). After cleaning: the last adults should be gone within about 9 days — up to 2 days for pupae to emerge plus 7 days of adult life.
Drain fly lifespan: how long do drain flies live?
Only a few days as adults. The University of Kentucky gives an adult lifespan of 3 to 4 days, and University of Florida researchers note that unmated females can live up to seven days while males last only a few days. So how long does a drain fly live? About half a week, typically — less than a fungus gnat and far less than a fruit fly.
That short lifespan of drain fly adults is what makes the calculator useful. If you're still seeing them weeks after cleaning, you're not looking at the same flies: a steady stream of new adults means the larvae still have somewhere to grow. Adults feed only on nectar and fluids from decaying sources (University of Kentucky), so it's the drain film, not the adults, that keeps an infestation going.
The same answer covers how long do sewer flies live and the moth fly lifespan: these are other names for the same family of flies (below). Adults rest on walls near the drain by day and become more active in the evening (Clemson HGIC).
Drain fly life cycle
The drain fly life cycle runs through egg, three larval stages, pupa and adult, all inside or right next to the drain. Every stage except the adult lives in the slimy, gelatinous film that builds up in drains and sewers (Clemson HGIC).
| Stage | How long | Notes |
|---|---|---|
| Egg | Hatch in under 2 days at 70 °F (21 °C) (UF/IFAS); within 48 hours at about 70 °F (UKy) | 10–100 eggs in a cluster (UKy); masses of 15–40, up to 100 (UF/IFAS) |
| Larva (3 stages) | 9–15 days at 21 °C, as few as 8 at 85 °F (29.5 °C) (UF/IFAS); 8–24 days depending on temperature (UKy) | Feeds on decaying matter, bacteria, mould and algae in drain film (UKy) |
| Pupa | 24–48 hours (UF/IFAS); adults emerge within 20–48 hours (UKy) | Looks like the larva (Clemson HGIC) |
| Adult | 3–4 days (UKy); unmated females up to 7 (UF/IFAS) | Rests on walls near the drain; mates and lays eggs |
| Egg to adult | About 11–19 days at about 21 °C (UF/IFAS stage times added together) | The figure this calculator uses |
| Whole life cycle | About 10–15 days at about 70 °F (UKy ENTFACT-615); typically 21–27 days (UF/IFAS); as little as 2 weeks in some species (Clemson) | Published totals differ by species and conditions |
Drain fly eggs
Drain fly eggs are laid in clusters of 10 to 100, are "rice-like" and cream to brown, and hatch within about 48 hours at 70 °F (University of Kentucky). Females lay them "on the surface of gelatinous film found in drains and sewers" (Clemson HGIC) — which is why cleaning has to remove the film, not just rinse the pipe.
Drain fly larvae
Drain fly larvae are long, skinny and legless, about 1/8 to 3/8 inch long, with a pale underside and a darker head, tail and bands across the back; they breathe through a tube that lets them survive in very wet places (Clemson HGIC). They can trap air bubbles and stay submerged for a day or more, so they're hard to drown (University of Kentucky ENTFACT-615). Grey larvae wriggling in standing water are a sure sign. Not sure what you've found? The larvae identifier tells drain fly larvae from fruit fly and fungus gnat larvae.
Sewer flies, moth flies and sink flies: same insect?
Yes. Clemson Extension lists the common names as "moth flies, drain flies, filter flies, sewer flies", all in the family Psychodidae; the University of Kentucky uses "drain flies (filter flies or moth flies)". The names describe where people meet them:
- Moth fly — for their fuzzy, moth-like wings, held roof-like over the body (Clemson HGIC).
- Drain fly and sink fly — for the household drains they breed in ("sink fly" is an informal name we didn't find in an extension source).
- Sewer fly — for sewers and sewage, where they also breed (University of Kentucky).
- Filter fly — for sewage filters, where the larvae also breed; the University of Kentucky notes that sewage filters can be flooded for 24 hours to kill them.
Whatever you call them, they're harmless nuisances: drain flies don't bite (Clemson HGIC), though they can carry bacteria from where they breed to where people are.
How long does a drain fly infestation last?
How long does a drain fly infestation last? As long as the breeding film is there. Once you scrub the drain, the countdown is short: pupae already in the pipe can still emerge for up to about 2 days, and those adults live up to 7 days, so the last flies should be gone about 9 days after a thorough clean. If you still see new drain flies after that, there's another source — a second drain, a seldom-used toilet, the drip pan under the fridge or a wet spot outside.
Do drain flies go away on their own?
Sometimes. Do drain flies go away on their own? The University of Kentucky says small infestations usually end once water flows normally through toilets and drain traps again — the typical case after a vacation. But "finding many flies over several weeks usually means a relatively permanent breeding site", and that needs cleaning or a plumber.
How long can drain flies live without water?
We found no study that timed how long drain flies can live without water, so we don't give a number. What the sources do say is that drain flies breed "most anywhere that water accumulates for a week or more" (University of Kentucky ENTFACT-615), and that the larvae need moisture. Drying out a breeding spot is part of the cure; the adults live only days whatever you do.
How to get rid of drain flies for good
Cleaning the breeding film is the cure; the University of Kentucky notes that pesticides are usually unnecessary once the source is found and removed. These non-toxic steps come from extension services:
- Find the drain first. Tape a clear plastic bag over the opening overnight, or invert a clear cup lightly coated with vegetable oil over it for several days; trapped flies mark the source (University of Kentucky). Our drain tape test planner sets it up for every drain.
- Scrub out the film. "The most effective control method is to clean pipes and traps thoroughly to remove accumulated slime" (University of Kentucky ENTFACT-615). Use a stiff or pipe brush (Clemson HGIC; UF/IFAS).
- Flush with very hot water after scrubbing; enzyme cleaners, baking soda or vinegar can help first (University of Kentucky). Hot water alone gives only short-term control.
- Run water through seldom-used drains and flush unused toilets regularly (University of Kentucky).
- Check outdoor wet spots where air-conditioning units drain and clogged gutters (University of Kentucky).
- Call a plumber if flies persist: broken pipes or moisture problems can be the cause (Clemson HGIC).
Don't pour insecticides down drains (University of Kentucky), and don't rely on bleach: NC State notes that bleach and standard cleaners won't kill larvae living in drain biofilm.
How this calculator works
The adult lifespan (3–7 days) and egg-to-adult time come from the same drain fly data as our gnat lifespan and gnats in winter calculators: UF/IFAS stage times at about 21 °C (egg 1–2 days, larva 9–15, pupa 1–2), giving 11–19 days from egg to adult. We found no drain fly development times at other room temperatures, so the same figures are used across 11–30 °C and the result notes that warmer rooms are faster (larvae in as few as 8 days at 29.5 °C) and cooler ones slower.
If you've cleaned the drain, the end date is your cleaning date plus up to 2 days for pupae already in the pipe to emerge, plus the longest adult lifespan (7 days): 9 days in all. If you haven't, the status is "Still breeding" until you do. With more than one drain, the date only holds when every one of them has been cleaned, and the result reminds you to test each. Cleaning dates in the future are rejected.
Frequently asked questions
How long do drain flies live?
Adults live 3–4 days (University of Kentucky); unmated females up to 7 days (UF/IFAS). New ones keep appearing until the drain film they breed in is cleaned out.
How long does a drain fly live from egg to death?
About 11–19 days from egg to adult at about 21 °C, plus 3–7 days as an adult — roughly two to four weeks in all.
How long do sewer flies live?
The same as drain flies — sewer fly, moth fly and filter fly are other names for them. Adults live about 3–4 days, up to 7 (University of Kentucky; UF/IFAS).
What is the drain fly life cycle?
Egg (hatching in about 2 days), three larval stages over about 8–24 days, a pupa of 1–2 days, then an adult that lives a few days. UKy gives about 10–15 days in all at 70 °F.
How long does a drain fly infestation last after cleaning?
About 9 days: pupae can still emerge for up to 2 days, then adults live up to 7. If flies persist, another drain is breeding them.
Do drain flies go away on their own?
Small infestations often do once water flows normally through the drains again (University of Kentucky). Many flies over several weeks means a permanent breeding site that needs cleaning.
How long can drain flies live without water?
We found no study that measured it. Larvae need moisture and can survive submerged for a day or more (University of Kentucky); adults live only days anyway.
What do drain fly larvae look like?
Long, skinny and legless, 1/8–3/8 inch, with a pale underside, darker head and tail and a breathing tube (Clemson HGIC). They're often grey and wriggling in water.
Where do drain flies lay eggs?
On the surface of the gelatinous film in drains and sewers (Clemson HGIC), and anywhere water stands for a week or more (University of Kentucky).
Does pouring boiling water kill drain flies?
It helps only briefly. Scrub the slime out with a brush first, then flush with very hot water (University of Kentucky; Clemson HGIC).
These calculators give estimates for education. Real flies vary with strain, food, humidity and temperature. For a stubborn infestation, your local cooperative extension service can help identify the insect. We give no pesticide advice.