Insects like flies and cockroaches are commonly considered the most disgusting insect pests to find within a home, but anyone who has ever experienced an infestation of moth flies may disagree. Moth flies are abundant in sewer systems where they proliferate in massive numbers, resulting in occasional pest disturbances during sewer maintenance work. Although they are repulsive pests, moth flies are also considered beneficial in sewage systems due to their habit of consuming sludge that often obstructs sewage conduits. Of course, moth flies are not just pests within sewer systems, as sewer dwelling moth flies often swarm through plumbing before emerging from indoor bathtub, sink and basement drains. Due to the excessively small size of moth flies, thick indoor swarms sometimes see residents inhale the filthy pests despite making every attempt to avoid doing so.

Several species of moth fly have been documented, and not all inhabit sewer systems and septic tanks, but all species are generally associated with breeding in environments where decaying organic matter is ubiquitous. Moth flies are not considered pests unless a human finds his or herself in the thick of a swarm, which often sees the tiny airborne insects fly into the nose, ears, eyes and mouth. In some indoor infestation cases, swarms may emerge from indoor drains repeatedly where they terrorize a home’s occupants. Moth flies may also maintain a lasting presence within drain pipes in homes. It is not uncommon for moth flies to emerge in massive numbers from manholes and storm drains before swarming into a home/s. When moth flies emerge from bathtub or kitchen drains, there is little that a resident can do to avoid keeping the pests out of their mouths and other orifices, but due to their weak flying ability, the pests tend to rest on walls after moving into other areas of a home.

The most common moth fly species in Massachusetts homes, Psychoda alternata, enters homes in large numbers where females lay hundreds of eggs each that hatch within 2 days. Larvae reach adulthood in a little over two weeks within indoor conditions. Moth flies of this species only grow to a minute 2 mm in length, and their habit of swarming around porch lights makes them a serious nuisance, but luckily, they do not transmit diseases to humans.

Have you ever seen any type of airborne insect pest emerge from an indoor drain?