Pest Profile: Fungus Gnats

The Tiny Fungus Gnat

As colder weather approaches, some outdoor plants are now getting chilly and need to be brought inside. Although moving plants indoors is great for keeping them alive, this can bring in some unwanted house guests, specifically fungus gnats. The fungus gnat is a small fly that enjoys eating fungus and decaying organic matter that often grows in the soil of these potted plants. There are about 65 different species here in North America, and they are found on all other continents and most of the major islands.

The larvae of this species are white, slender, and legless with a black head and smooth, semi-transparent skin. When the larvae are fully grown, they are about 1/4″ long. At no more than 1/8″ long, the adults are rather small when fully grown. They are delicate flies with dark brown bodies, dusky wings, a small head, and rounded, moderately prominent eyes that meet above the bases of their thread-like antennae. Their legs and wings are relatively long for their size. These little critters more closely resemble tiny mosquitoes than common flies.

Although small, these flies can be a huge nuisance, so how can we help to control them in our homes? Normally fungus gnat problems may result from overly wet conditions and diseased roots. When watering indoor plants, it is important to make sure that their pots are able to drain. Plants that retain too much water will grow fungi, which is what feeds the fungus gnats. Also, if you store any potting material, be sure to keep it in a dry place where it will not be subject to wet conditions. Fungus gnats are not limited to eating fungi on indoor plants; they also feast on fungus and algae that grow on outdoor furniture such as benches. All that is to say, if fungus gnats are in your home, it is important to identify the source of these flies. Removing sources and/or drying out the plant(s) which they are feeding on and breeding on are key factors in helping to control these pests.

Kristen Stevens, BCE