Individually, midges and gnats would hardly be noticed in the garden, but when they form large clouds or swarms, that attracts attention. As many of these species look like mosquitoes, this also increases concerns of gardeners. Midges and gnats are common names for a large number of small, non-biting flies. The immature stages develop within water in pools, containers, ponds, clogged rain gutters, or in some cases, wet soil or seepage areas. Most feed on living or decaying plant matter and are an important part of aquatic food chains. Many species can survive in very stagnant or polluted water.
Large mating swarms of adults often appear about dusk and may occur for several days, especially after a prolonged wet period. These swarms often are centered a couple of feet above a noticeable object in the yard, such as a stone or potted plant. Gnats may be attracted to lights at night and become a nuisance, landing on people or entering homes. But remember, these tiny flies do not feed. They only live long enough to mate and lay eggs. Masses of eggs are laid in water or on aquatic vegetation. The life cycle usually takes about 4 to 5 weeks. There may be several generations during the summer, but these insects usually disappear with the onset of dry weather. Fortunately, problems are usually temporary and intermittent.
There are few good alternatives for control of the adults, other than some pressurized aerosol sprays containing pyrethrins. These are impractical for treating anything other than small areas. These products only kill insects directly hit by spray particles; there is no lasting or residual effect once sprays dry. More gnats will quickly re-enter the area after the spray has settled.
The gnats rest on vegetation and in grass during the day, so an application of a malathion spray may reduce numbers somewhat. Gnats and midges attracted to lights at night may be reduced by replacing white lights with yellow.
Long-term control requires trying to eliminate breeding sites by draining wet areas or eliminating standing water. While this may not be practical, water cannot be treated with insecticides in an attempt to control gnats. The potential environmental harm is too great to justify an application for a temporary nuisance.
Always read and follow the labelling directions for pesticides.
By Ric Bessin, Entomology Extension Specialist