Do Drain Flies Die in Winter

Most fly species cannot survive outside temperatures below 32°F (0°C). They die unless they find a warm and conducive place to overwinter, such as your home.

Drain flies are one of the few insects that can tolerate cold weather conditions. They have a thick layer of fat that helps them keep warm and insulated, giving them the energy to stay active in colder temperatures.

Drain fly larvae can survive freezing temperatures since they hardly need oxygen and can enter a state of hibernation for the winter. Also, they can remain below the gelatinous film formed in drains for long periods. However, both adults and larvae have zero chance of surviving extremely low temperatures.

icicles on a home

Temperature affects drain flies’ survival and the rate at which they mature. For example, cold weather tends to slow down the biological processes of drain flies. It may take longer for their eggs to hatch or for larvae to mature. On the other hand, warmer temperatures accelerate their pupal stage and life cycle.

What are drain flies?

Drain flies, also known as moth, filter, sink, or sewer flies, are tiny gnats measuring about 2mm to 5mm. Their color ranges from pale gray to black. They have round, fuzzy bodies with moth-like wings and are poor fliers—they often move around by hopping from surface to surface instead of buzzing around the house like other pests.

image of a drain fly

These sewer flies have a lifespan of between 8 and 24 days, but an adult female can lay up to 100 eggs in 24 hours. So, if you notice any drain flies around your home, it is vital to get rid of them before you end up with an infestation.

What causes drain flies?

Drain flies thrive in moist environments with organic matter, such as in stagnant water. You can find them almost anywhere where water has accumulated for a week or more, but they typically enter buildings or your home through basements, windows, and drains.

clogged drain

Common drain fly sources in your home include slow or clogged drains, shower drains, infrequently used toilet bowls and tanks, refrigerator drain pans, and stagnant water from leaking pipes. You might also find drain flies around sinks, sewers, septic tanks, sewage-contaminated soil, wet mops, buckets, compost piles, storm drains with standing water, and wet areas around the garbage, birdbaths, or barns.

What do drain flies eat?

These flies feed on organic matter in low, stagnant water, which is why drains are ideal for them to thrive and reproduce.

What is the life cycle of a drain fly?

drain fly larva and pupa

The life cycle of a drain fly includes the egg, larval, pupal, and adult stages. Once the adult females lay eggs, the eggs hatch into larvae within 48 hours. The larval stage lasts between 8 and 24 days, depending on the temperature and availability of food. The pupal stage takes up to 40 hours, and adult flies will live up to two weeks.

Can drain flies survive winter?

These flies thrive in warm, moist places, which is why you can easily spot them in the summertime or in areas with mild year-round climates.

If temperatures fall below freezing, and drain flies don’t find a warm place to overwinter, they will die. But, drain worms (the larvae) can still survive by staying below the gelatinous film in drains. They will thrive all year round if the cold temperatures don’t reach them.

If adult drain flies do find a place to overwinter, they can continue with their life cycle as normal, even during the winter. They will only emerge once it starts getting warmer outside. But colder temperatures can still stunt their rate of reproduction even with the ideal spot to overwinter.

Do drain flies hibernate? Are they seasonal?


Cold temperatures significantly slow down the biological processes of drain flies. For example, drain fly eggs will hatch more slowly in cold weather, which suggests that they may stay dormant until warmer weather returns. However, in places where the cold doesn’t reach them, they can be alive all year round.