Pest Of The Week – Filter Flies

Adult filter flies are tiny, around 2mm in width. They appear to be fuzzy, dark or greyish insects with the body and wings densely covered with hairs. The wings, which appear too large for the body, are held roof-like over the body when at rest giving a moth-like appearance.

Life Cycle
Filter flies breed in polluted, shallow water or highly moist organic solids. Both mated and non-mated females lay eggs. Egg masses contain 30 to 100 eggs, which hatch in less than 48 hours into small (3/8 inch), legless larvae that are pale in the middle and darker on the ends. Filter fly larvae and pupae live in the thin film found in drains and septic tank field lines and on filter stones. The larvae feed on fungi, bacteria, algae and other microorganisms found in the liquid or slime layers that develop around debris in drains, sewage treatment beds and standing water. When food is scarce, they can become cannibalistic. Larvae can survive temperature extremes and habitats low in oxygen. The larval stage lasts 8 to 24 days and the pupal stage 1 to 2 days. Adults live only 3 to 4 days without food, but can survive for 1 to 3 weeks if nectar or other liquid carbohydrate foods are available.

Filter fly larvae are actually beneficial because they break down organic waste into water soluble compounds. Adult flies, however, are a nuisance. They cannot bite, but they may become so numerous indoors that they congregate at windows and around light fixtures, showers, bathtubs, sinks and floor drains.
The key to solving a filter fly problem is to find and eliminate the source—that is, the areas where excess moisture and organic debris have built up. If there are lots of adult flies inside a drain the drain is probably a breeding site. To check for breeding sites, place a length of tape across drains (or cracks in the floor) without totally covering the opening. (If the opening is totally covered, there will be no air flow and flies will not emerge.) Check the tape periodically. If you see flies stuck to the tape, you have found a source of infestation.
Once located, the larval breeding sites should be eliminated by cleaning to remove any organic matter. Household insecticides can be used to control adult sewage filter flies, but the effects will be very temporary unless the source of the larvae is also removed.

If you suspect you have a filter fly infestation in Edinburgh, Glasgow, Aberdeen, Dundee or Perth, call GRAHAM pest control today and we could help.