There are many different types of flies you can experience in your home, and chances are you’ve come across one or two. One type of fly that can be particularly pesky is the drain fly. If you’ve ever seen these little insects flying or resting around your kitchen or bathroom sink, you’ve probably wondered what causes them. Keep reading to find out—and if you learn what causes them, it’s easier to know how to prevent them.

What does a drain fly look like?


As we mentioned, there are several different types of flies you might encounter in your home, so it’s helpful to be able to tell them apart. Drain flies have a fairly distinct appearance, with their fuzzy-looking wings and weak flying. They often exhibit short, hopping bursts of flight and are not very fast in the air. They are sometimes called moth flies because of their similar physical attributes. Below is a breakdown of the identifying characteristics of the drain fly:


  1. Anywhere from 1/16 to ¼ of an inch, with many about ⅙ of an inch
  2. Dark, winged bodies ranging from gray to a dark brownish-black
  3. Wings covered in fine hairs (which is why they look similar to moths)

What causes drain flies?

Drain flies are attracted to standing water and moist decaying organic matter, hence their common name “drain fly.” Like gnats and mosquitoes, drain flies breed in water. Specifically, drain flies breed in areas with shallow, dirty water and organic material such a s food waste. This is because drain fly larvae feed on muck and the buildup o f organic materials. Drain flies lay eggs in irregular numbers, laying anywhere from 10 to 200 eggs at one time. After eggs are laid, they hatch in about two days. Then, they spend the next 9 to 15 da ys in the larval stage feeding and developing before entering the pupal stage for 20 to 40 hours; then, they finally emerge as adults. The life cycle can be completed in as little as eight days but ca n take as long as 24 days depending on temperature and other environmental conditions. Adults will feed on the same organic material that larvae feed on, with the addition of flower nectar.

Drain flies can infest both homes and commercial properties—including sewage treatment plants. Around commercial properties they can sometimes be found underneath air conditioning units. In your house, you’re often more likely to find drain flies after being away from your home for some time, after there has been time for water to remain standing. If this is the case, there is a good chance that the drain fly issue will resolve after you’ve resumed normal activities and water begins to move again. However, this may not be the case if you’re dealing with many drain flies. And while it is common to find drain flies after periods of being away from your home, you don’t have to go on vacation to find yourself with these fuzzy little flies. Other areas in and around your home where you may find drain flies include:

  1. Infrequently used bathrooms
  2. Air conditioner pipes
  3. Toilet tank
  4. Moist compost
  5. Dirty garbage cans
  6. Places where rainwater collects, such as tree holes

While drain flies aren’t known to bite humans, they can still cause health hazards if someone breathes in dust or fragments of dead drain flies. Additionally, they might transmit microbes picked up from the filthy areas that they live and breed in.