Moth flies (which are also known as drain flies, sewer flies or filter flies) possess hairy, moth-like wings and are very small at less than one-tenth inch in length on average. These minute insects lay their eggs in soggy organic matter, including raw sewage, and you'll typically spot them hovering around sinks, bathtubs, toilets and drains. Needless to say, the moth fly's germ-ridden diet (primarily algae, bacteria and fungi) makes it an unsuitable and unsanitary houseguest for humans.