Drain or Moth Flies

What are drain flies?

These tiny (~1/10") dark colored flies are sometimes common in homes near bathroom or kitchen drains. The flies are harmless but can be nuisance if present in large numbers. Drain fly larvae develop in the gelatinous organic slime (scum, gunk) that often accumulates in drains or sewage ponds. The flies can also be common around cold-composted compost bins.

Drain flies, also called moth flies because of the moth-like scales that cover their wings, belong to the fly family Psychodidae. A related fly in this same family, called the sand fly, is responsible for transmitting the disease Leishmaniasis. Leishmaniasis not occur in the US.

Control of drain flies

The best and safest way to control drain flies is to remove the gelatinous, often black, "gunk" that builds up in drains. This is the material on which drain fly larvae develop. Drains can be cleaned with a brush or one of the new enzyme/bacterial drain cleaners. It is not necessary to apply insecticides to control flies. Once the drains are cleaned the flies will go away.

Drain cleaner types

Clogged drains should be cleaned with a chemical drain cleaner such as the old standby Drano (tm) because the enzyme/bacterial drain cleaners won't work on clogs. The enzyme-based/biodegradable products are intended to remove the gelatinous film only. Use these cleaners several times a year in all drains to keep ahead of the gunk buildup.