Drain flies deposit their eggs in decaying organic matter found in sewage, filter beds, drains and waste waters. Adult flies appear in 5-14 days. In warm buildings, they continue to develop throughout the winter. Adult flies are found primarily in damp places like basements, but individuals may stray into other areas of the house. Neither the adults nor the larvae are harmful, but their presence may be a nuisance.
Sanitation is the best control measure for drain flies.
Clean out the overflow drains, drain traps and basement drains. Avoid moist debris of any nature, especially in the basement, and do not allow wet lint to accumulate under washing machines. Chemical control Use chemicals only after solving sanitation problems. Pour commercial drain cleaners, rubbing alcohol, household bleach or boiling water into overflow drains to eliminate maggots. To control adult drain flies, use household aerosol insecticides containing pyrethrin.