Drain flies are common household pests often found congregating near sinks, showers, and other drainage areas. Their presence can be a nuisance, and many people wonder about their potential to cause harm. Understanding these small insects, from their basic biology to effective elimination strategies, can help manage their presence in a home environment.
Do Drain Flies Bite Humans?
Drain flies do not bite or sting humans or animals. Their mouthparts are designed for siphoning liquids, such as decaying organic matter and polluted water, rather than for piercing skin. Any perceived “bite” from a drain fly is likely a misidentification of another insect. While drain flies are harmless, their decaying bodies can cause allergic reactions in some individuals. Fragments and dust from their bodies may also trigger asthma symptoms in susceptible people.
Understanding Drain Flies
Drain flies, also known as moth flies or sewer flies, belong to the insect family Psychodidae. These small insects typically measure about 1/8 inch (1.5 to 5 mm) in length. They have small, hairy bodies that appear fuzzy, with wings also covered in dense hairs, often held in a roof-like position over their bodies when at rest. Their flight is short, erratic, or hopping, as they are not strong fliers and tend to stay close to their breeding sites. Drain flies prefer damp habitats rich in decaying organic matter, such as the gelatinous film found in drains, sewers, septic tanks, and moist compost piles.
Females lay between 15 and 100 eggs in these moist environments, with eggs hatching within 30 to 48 hours. The legless, worm-like larvae feed on bacteria, fungi, and other microorganisms within the organic film for 8 to 24 days. After maturing, they enter a pupal stage for one to two days before emerging as adult flies. The entire life cycle from egg to adult can be completed in about one to three weeks.
Effective Drain Fly Elimination
Eliminating drain flies primarily involves removing their breeding source, which is typically the organic film or sludge in drains. Simply killing adult flies with sprays provides only temporary relief, as new flies will continue to emerge from untreated breeding sites.
Begin by pouring boiling water down the suspected drain, repeating this process daily for several days. This loosens and flushes away organic buildup. For more effective removal, use a long-handled brush for cleaning pipes to scrub the inside surfaces of the drain and trap. This dislodges the gelatinous film where larvae feed and eggs are laid.
Enzymatic drain cleaners can also be highly effective, as they contain enzymes that break down organic matter in drains. These products cling to pipe walls, working over several hours to eliminate the flies’ food source. Unlike harsh chemical cleaners, enzymatic solutions are safer for plumbing and the environment.
Addressing other sources of standing water or decaying organic material is important. This includes fixing leaky pipes, cleaning dirty garbage cans, and removing standing water from plant saucers. Regular maintenance, like periodically flushing and cleaning drains, prevents future infestations.