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Drain Flies

Drain Fly Control: Protect Your Home or Business


  • People often refer to the pests as moth flies, filter flies, and sewage flies.
  • These insects are not strong fliers and can only travel a few feet at a time.
  • Females can lay anywhere from 10 to 200 eggs.


Most drain flies are less than a quarter-inch in length. The flying insects have dark gray bodies and hairy wings that give them a fuzzy appearance. Some species extend their wings to the side, and people often mistake them for moths.

Drain fly eggs are brown or cream-colored and typically hatch within 32 to 48 hours. Upon hatching, pale white larvae emerge from the eggs and begin feeding on organic material. These tiny, worm-like larvae also have black bands across their body segments.

How Do Drain Flies Get Inside Buildings?

Adult drain flies are small enough to squeeze through mesh screens and gaps around doors or windows. Eateries with bright outdoor light fixtures above the entrance often attract the insects, too. Plumbers and water treatment workers may also come into contact with drain flies and accidentally carry them home or to other job sites.

Signs of Drain Fly Infestation

  • Sightings – Seeing just one or two drain flies in your sink isn’t always a serious issue. However, the pests reproduce rapidly, so it could become cause for concern.
  • Larvae – Female drain flies lay eggs in wet, rotting organic matter, like the moist build-up found inside drains. You may see larvae floating in the water after turning on the faucet in a clogged sink or bathtub.

Problems Caused by Drain Flies

Drain flies do not bite, but these pests do mate and lay eggs in pipe sludge, sewage, and manure. When they infest homes, restaurants, or cafeterias, the insects spread bacteria wherever they land. Also, drain flies can aggravate asthma and cause allergic reactions. When a large number of flies die in one place, their decomposing bodies form allergens, which affect people sensitive to them.

Standing water in toilets provides prime drain fly breeding grounds. Vacationing homeowners and building managers with vacant units often have to contend with unexpected infestations. In hotels, guests who see the pests in a shower or tub may also leave poor reviews. Drain flies can also compromise sterile settings and clean rooms in health care, tech, and pharmaceutical industries.

Prevention Tips

The most effective way to prevent a drain fly infestation is to ensure drains and traps are clean. Removing build-up takes away the larvae’s main food source and prevents adults from laying eggs. If you suspect a drain fly problem in your home or business, call the trusted experts at Western Pest Services or contact us online.

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