Gnats, small, winged insects, are common and often mistaken for other tiny pests. They are part of the Diptera order, sharing characteristics with mosquitoes and midges, but possess distinct features. These insects are typically small, 1/16 to 1/8 inch long, with varied appearances across species. Their ubiquitous presence means they can appear seemingly out of nowhere, hovering indoors and outdoors.
Understanding Gnat Flight Behavior
Gnats exhibit erratic, seemingly aimless flight, especially when disturbed or in large groups. Their small size and delicate wings contribute to their weak flying ability, meaning they generally do not travel long distances. Gnats are often observed in swarms or “clouds,” a behavior primarily linked to reproduction. Male gnats form these swarms to attract females for mating.
Swarms frequently form around visual markers that contrast with the surrounding landscape, such as fence posts or ripples above water, which helps females locate them. Gnats are also drawn to sources of moisture, decaying organic matter, and sweet scents. This attraction explains why they might hover around damp areas, overripe fruit, or even human faces, seeking moisture from sweat or breath. Their attraction to light sources also means they are often seen near windows or artificial lights, particularly at night.
Common Types of Flying Gnats
Many small flying insects are broadly referred to as “gnats,” but several specific types are commonly encountered. Understanding these distinctions helps in identifying the particular nuisance.
Fungus Gnats
Fungus gnats are small, dark flies, 1/16 to 1/8 inch long, with slender legs and long antennae. They thrive in moist soil, often near overwatered houseplants, where they lay eggs. Adult fungus gnats are weak fliers and tend to remain close to plants, often seen resting on the soil or foliage. Their larvae feed on fungi, algae, and decaying organic matter in the soil, sometimes damaging roots.
Drain Flies (Moth Flies)
Drain flies, also known as moth flies, are small, fuzzy insects with short, hairy bodies and moth-like wings. They are 1.5 to 5 millimeters long, often brown, gray, or black. They breed in gelatinous organic buildup in drains, septic tanks, and other moist areas with decaying matter. Drain flies are weak fliers, making short, hopping flights, often resting on walls near breeding sites.
Biting Midges (No-See-Ums)
Biting midges, commonly called “no-see-ums,” are exceptionally tiny, often less than 1/8 inch long, making them difficult to spot. They are found in outdoor habitats like swamps, marshes, and damp areas near water sources. Female biting midges are known for painful bites, requiring blood meals to produce eggs. They are most active during dawn and dusk and can pass through standard window screens due to their minuscule size.
Effective Gnat Management
Managing gnat populations involves targeting their breeding sources and reducing their attractants. Different strategies are effective for various gnat types.
For fungus gnats, controlling moisture in plant soil is important. Allowing the top 1-2 inches of soil to dry between waterings disrupts their life cycle, as larvae cannot survive in dry conditions. Yellow sticky traps near plants capture adult gnats, reducing egg-laying females. Products containing Bacillus thuringiensis israelensis (BTI), a naturally occurring bacterium, can be added to water to kill larvae in the soil.
To address drain flies:
Thorough drain cleaning eliminates the organic film where they breed.
Pouring boiling water down drains removes buildup.
A mixture of baking soda and vinegar, followed by boiling water, also breaks down organic matter in pipes.
Using a pipe brush to scrub drains and regularly cleaning sink and shower drains removes breeding sites.
Controlling biting midges often focuses on personal protection and environmental management. Applying insect repellents with DEET, picaridin, or oil of lemon eucalyptus deters bites. Avoiding outdoor activities during peak biting times (dawn and dusk) reduces exposure. Installing fine-mesh screens on windows and doors prevents these tiny insects from entering indoors.
General gnat management practices include good sanitation by promptly discarding decaying organic matter and sealing home entry points. Removing standing water and ensuring proper drainage also reduces potential breeding grounds.