Drain Flies

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Drain Flies

Drain flies are small flying insects that belong to the mosquito family. They are also called cesspool moths, latrine flies or sewer flies. You can encounter them outdoors, but they are quite small, making them especially noticeable when they bother us indoors. Unlike other mosquitoes, the moth fly does not sting. Also, your clothes have nothing to fear because the drain fly is not a real moth. The drain fly is called this way because of its shape and hairy appearance. Because the drain fly mainly eats and lives in very unsanitary places such as sewers, among others, they are disease spreaders.

The small animal can become a real pest and they can indirectly transmit disease by feeding on organic decaying material, fungi and bacteria. Since a the female can lay as many as 10 to 200 eggs a day, it is wise to control the little tormentors as soon as possible. They are unsanitary and therefore an unwelcome guest in our households or business premises.

Species of drain flies

There are a number of different species of drain fly worldwide but the two most common species are theTinearia alternata and the Clogmia albipunctata. Both species are found almost all over the world. For both species, they like to live in our drainage systems since there is plenty of bacteria, fungi and decaying material to be found there.

Living Environment of a drain fly

The habitat of the drain fly is also immediately the reason why they can be an indirect danger because they can transmit diseases. This is because they often live in the sewers and in the water drains of our sinks, showers, bathtubs and toilets. In these places, they often sit on feces and other decaying organic material that intentionally or unintentionally disappears down the drain through our sink or toilet. Dung piles and standing water are also places where the drain fly likes to hang out. The drain fly is most active when it is dusk or dark. So if you see one or more drain flies flying around near your drain during the day, you can unfortunately assume that out of sight there are many more drain flies and larvae.

Drain fly in the US

Drain flies are increasingly becoming a pest within US households and businesses. This has to do with the increasingly hot summer days in our country. The warm days are ideal for the drain fly. They reproduce even faster and the female lays more eggs than in cold periods. The insect is common in the wild in the tropics and subtropics. Our winters would soon be too cold, but indoors the drain fly thrives (too) well all year round in the Netherlands as well. You often see them flying or crawling around drains, toilets and sink drains.

Outward characteristics of a drain fly

The drain fly looks like a small hairy moth although it is actually a short stocky and hairy mosquito species. The triangular shape of its wings makes it look even more like a moth. They are not the best fliers. They fly in irregular trajectories and are also not very fast. From feeler antenna to abdomen, the creature is covered with fine hairs. The drain fly has a gray-brown to sometimes almost black color. They are usually between 1.5 and 4 millimeters in size.


The head of the drain fly also has all the appearance of a moth. Unlike the mosquitoes we know, the head is blunt and hairy. The antennae or feelers on the head are also hairy. If you were to hold the drain flies head under a magnifying glass you will discover that it has a similar stinging and sucking mouth as the more familiar mosquito species. However, the drain fly has no interest in human blood.


The thorax of the drain fly is also hairy and resembles that of a moth. Attached to the thorax are the wings. When at rest, the wings are folded backward and form a heart-shaped whole.

Back body

The drain fly has a short stocky abdomen. The abdomen also has tiny hairs. Because the animal is very hairy, its downy hairs drag all kinds of bacteria into households and businesses with ease. The abdomen has no sting.

The larvae

You won’t see them easily because they usually hide in the sewage and drainage system of buildings. The larvae look like tiny worms that are about 9 millimeters long. They have a white-gray color and the ends are slightly darker.

Similar insects

The drain fly (or moth fly, cesspool moth, sewer gnat or sewer fly) is not so easily compared to other insects. It can suddenly fly irritatingly through the kitchen or fly up from your drain or toilet. Like fruit flies and other flying insects, they are irritating house guests, but of a greater caliber and pose greater dangers.


The drain fly likes heat. Preferably even sweltering warmth. Because it lives on bacteria, fungi and decaying organic matter, the drain fly seeks out the dirtiest places to feed and lay its eggs. Therefore, its other names such as sewer fly, toilet moth, and sewer mosquito did not come out of nowhere.

What does a drain fly eat?

The diet of the drain fly includes human and animal feces. Fungi and rotting organic matter, cadaver meat, rotting fruits and vegetables. Basically anything as long as a lot of bacteria or fungi grow on it. In short, all kinds of things we as humans prefer to stay far away from. The mosquito also likes to lay its eggs in the mud on the walls of sewers and drains. The larvae eat themselves full of the filth until they develop into full-grown moths.

Enemies of the drain fly

The drain fly is actually a non-native insect. Therefore, it has no known natural enemies in our country. The main enemy of the drain fly is probably humans, especially those who try to exterminate the beast.

Reproduction and Lifespan

The adult drain fly does not have a long life. After they turn from a pupa into a flying moth bug they have an average of 7 to 21 days before they die. During that time they mate as much as possible and, under ideal conditions, lay as many as 200 eggs per day. The worm-shaped larvae pupate relatively quickly. Pupation takes only 20 to 40 hours. Because a female lays up to 200 eggs per day, the drain fly can quickly become an unsanitary pest.

Nuisance & diseases

The nuisance caused by drain flies is perhaps the least of these and comparable to other flying insects. The major drawback of the drain fly is that it can transmit bacteria to food items with ease. It is therefore important to prevent bacterial contamination and banish drain fly from your home or business by exterminating them. Any problems with the sewer or your drains should be taken care of Sometimes drain flies can in fact be an indication that there is a leak somewhere.

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