I have little black insects coming out of my sink and bath drains: what are they?

Seeing insects in your home can conjure up images of disease and filth, especially when you see a large number of them. The tiny black insects that emerge from your bath and sink drains are commonly known as drain flies, although some call them drain moths, filter flies and sewer flies. Although drain flies generally do not transmit disease, you will want to remove them from your home permanently in case they do.

When drain flies become adults, they have a length of only 5 or 4 mm (1/5 to 1/6 inch) with a long antenna. Drain flies have long, grey hairs covering their tiny bodies, giving them the appearance of fuzzy moths. As you watch them fly, you will notice drain flies have a navigation problem, making uncontrolled flights that cover just a few metres. When drain flies sit, they hold their wings above their bodies like a roof.

The slimy, gelatinous drain and sewer walls contain from 30 to 200 drain fly eggs, which hatch at room temperature within 32 to 48 hours. As the larvae feeds, they mature in 9 to 15 days. Drain flies start out as oblong eggs, pale, elongated larvae with a suction cup under their bodies, pupae, and then adults. The complete life cycle of a drain fly takes one to three weeks. Adult drain flies live for two to three weeks.

Besides your sink and bath drains, you will find drain flies breeding in other places where moisture exists. For example, drain flies love breeding indoors in your sewer, dirty rubbish bins, wet mops and even the wet lint under your washing machine. These flies also breed in any standing water outdoors, in moist composts, your birdbaths and your air conditioner. Drain flies enter your home through the drainpipes of baths and sinks and through your window screens. Drain fly larvae eat bacteria from the walls of drainpipes and sewers, which has gelatinous material covering them. Adult flies enjoy consuming sugars in liquids, flower nectar and fruit juices.

If you see a drain fly infestation in your home, you need to get rid of their breeding site, which means stagnant water. Drain flies need stagnant water to reproduce. Since you have drain flies coming out of your sink and bath drains, you can start getting rid of these breeding sites by first cleaning out any build-up of debris and slime inside of your drains, the larvae food source. Use a noncorrosive bacterial gel rather than an insecticide to quickly get rid of all organic matter in your drains. You can find some gels made especially for safely eliminating drain flies. When you pour it down your drains, it clings to the sides of the pipes without harming any type of plumbing and will keep your drains flowing. Do not use bleach with the gel since bleach makes the bacterial gel ineffective. Also, clean out your rubbish bins and any standing water you can find, including the standing water in the trays under your houseplants.