The term “gnat” is a broad designation for several types of small, flying insects, only some of which bite humans. The gnats that cause bites are typically blood-feeding pests like biting midges (often called “no-see-ums” or sand flies) and black flies. These insects use scissor-like mouthparts to cut the skin and access blood. Biting gnats inject an anticoagulant compound in their saliva, causing the characteristic small, itchy, red bumps and localized swelling. Common household gnats, such as fungus gnats and drain flies, do not possess the mouthparts to pierce skin. Understanding whether the problem is biting gnats outdoors or nuisance gnats indoors is the first step in effective management.
Creating Personal Barriers
Immediate defense against biting gnats involves creating physical and chemical barriers, which is particularly helpful during peak activity times like dawn and dusk. Topical repellents are highly effective and feature ingredients such as DEET, Picaridin, and Oil of Lemon Eucalyptus (OLE). Repellent should be applied directly to exposed skin and clothing, following the manufacturer’s instructions carefully, and reapplied as needed.
Wearing long-sleeved shirts and long pants minimizes the available surface area for gnats to target, as they cannot bite through fabric. Light-colored clothing is preferred, since some biting insects are more attracted to darker colors.
For more intense protection, clothing and gear can be treated with permethrin, an insecticide that repels and kills insects upon contact. Physical screens, including fine-mesh head nets, offer immediate protection during outdoor work or recreation. Inside the home, ensuring window and door screens are tightly sealed prevents gnats from entering living spaces.
Eradicating Outdoor Breeding Areas
Long-term reduction of biting gnat populations focuses on eliminating or treating the environmental sources where they reproduce. Many biting species, like black flies, lay their eggs in or near running water, while others, like biting midges, breed in damp soil or decaying organic matter. Proactively managing standing water is important, as even small amounts can serve as a breeding site. This includes regularly emptying water from bird baths, flower pot saucers, and any containers that collect rainwater.
Yard maintenance plays a significant role in source reduction. Decaying leaves, wet mulch piles, and rotting logs provide ideal breeding habitats for certain gnat species. Removing this organic debris and addressing clogged gutters that trap water and decaying material can substantially decrease local populations. Avoiding outdoor activities during crepuscular hours, when gnats are most active, can also reduce exposure.
For water sources that cannot be eliminated, such as rain barrels or ornamental ponds, biological control agents can be used. Products containing Bacillus thuringiensis israelensis (Bti) are a specific larvicide that targets the larvae of gnats and mosquitoes. Bti is a naturally occurring soil bacterium that, when ingested, disrupts the larvae’s digestive system within 24 hours, effectively halting the reproductive cycle. This bacterium is harmless to humans, pets, fish, and beneficial insects.
Controlling Gnats in Indoor Environments
Indoor gnat problems are most often caused by non-biting species, primarily fungus gnats and drain flies, which are attracted to moisture and decaying organic material. These pests require specific control methods depending on their breeding location.
Fungus Gnats
Fungus gnats thrive in the moist soil of houseplants, where their larvae feed on organic matter and plant roots. To control these pests, it is necessary to let the top layer of potting soil dry out completely between waterings, which eliminates the moisture needed for the larvae to survive. For existing fungus gnat infestations, Bacillus thuringiensis israelensis (Bti) products, often sold as “Mosquito Bits,” can be applied to the soil. Mixing these granules with water to create a “Bti tea” and using it to water the plants will kill the larvae without harming the plant itself. Yellow sticky traps placed upright in the pots will capture adult gnats, helping to monitor and reduce the flying population.
Drain Flies
Drain flies, which have a fuzzy, moth-like appearance, breed in the organic sludge that accumulates in plumbing drains and garbage disposals. Eliminating this breeding material requires thoroughly cleaning the drains using a stiff brush and an enzymatic or biological drain cleaner designed to break down the organic film. Pouring boiling water down the drain can also help to flush out the sludge. General indoor trapping, such as a simple apple cider vinegar trap with a drop of dish soap, can capture adult gnats attracted to the fermentation odor. The soap breaks the surface tension of the liquid, causing the insects to drown. Reducing indoor humidity and ensuring that all entry points, such as seals around windows and doors, are intact will limit the overall presence of these moisture-seeking pests.