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Finding Fungus Gnat Breeding Sites

By Chris Williams on February 7, 2012.

Q. We’ve had a problem for several months with what I think are fungus gnats, small dark gnat-like flies that are often in your face. I know they usually come from house plants, but I can’t find any infested plants. I’ve let the soil in all my pots dry out but I still have gnats. What else could they be coming from?

A. You’re right about the house plants. When you have a problem with fungus gnats indoors, the first place to check is potted plants. The most common source of this fly is overwatered house plants or large indoor planter boxes (in malls, hotel lobbies, and office buildings) that are kept constantly damp. The larvae feed in the upper layers of this damp soil, feeding on decaying organic matter. And the cure is to simply cut back on watering and let the soil dry out occasionally.

fungus-gnatHouse plants aren’t the only place to find breeding fungus gnats, however. Keep in mind that the larvae feed primarily on molds and rotting vegetation, so that tells you that you are looking for a site that stays damp. For example, outdoors, fungus gnats are found in damp, shady areas such as in piles of compost or leaf mold, rotting grass clippings, damp soil, rotting wood, even in bird or animal nests or in animal feces.

Fungus gnats can be serious problems in greenhouses or mushroom farms. Assuming that you don’t have either one in your home, these are some of the other possible indoor breeding sites:

·        areas around water leaks: near water stains, blistered paint, etc.

·        areas near leaky roofs

·        damp wall voids with new construction materials

·        indoor terrariums

·        stored compost or potting mix

·        accumulated bird droppings in bird cages

You’ll be looking for fungus gnat larvae which are whitish, worm-like, and legless, and about 1/4 inch long with a dark head. Adult flies will also be found in the vicinity of larval food sites. The adult flies are dark, with long legs and antennae, a pointed abdomen, and are about 1/8 inch long. They look somewhat like miniature mosquitoes, but of course, they don’t bite. The flies tend to run along surfaces in a jerky manner and most are attracted to windows and lights.

Fungus gnat adult flies only live about 10 days so that means you have an ongoing breeding source somewhere. The gnats you are seeing now are not gnats that emerged weeks earlier. It’s also possible that the gnats are breeding outside in sites like mulch or clogged gutters, are attracted to lights around your home, and are then finding their way inside. What you need is a thorough inspection by a pest management professional. Call Colonial. Our trained pest control technicians can find the source of your fungus gnats and can take care of the problem…guaranteed.

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