Gnats are a common presence in many environments. These small, winged insects are frequently encountered both indoors and outdoors, leading to concern regarding their impact on humans and plants. While often perceived as a nuisance due to their sheer numbers, understanding their actual threat level requires distinguishing between various types of gnats and their behaviors.
Identifying Gnats and Their Common Types
Gnats are a broad group of tiny, two-winged flies, typically measuring between 1/16 and 1/8 of an inch long. They possess slender bodies, six legs, and translucent wings, often holding their wings folded behind their backs when at rest. Despite their similar appearance, “gnat” is an umbrella term encompassing distinct species, each with unique characteristics and habitats.
Fungus gnats are common indoors, often found near houseplants. These dark-colored, slender gnats can be mistaken for small mosquitoes, though they do not bite. They thrive in moist potting soil and decaying organic matter, with females laying eggs in damp soil. Weak fliers, they remain close to breeding grounds, often seen hovering around plants or attracted to indoor lights.
Drain flies, also known as moth or sewer flies, are common household gnats. They are small, fuzzy insects with hairy bodies and rounded wings that rest in a roof-like manner. These flies breed in wet organic matter found in clogged drains, sewage systems, and moist compost. Weak fliers, they are typically found resting on walls near drains, becoming more active at night.
Fruit flies are often referred to as gnats, particularly in kitchens. These insects are usually tan or brownish with prominent red eyes and an oval body. They are attracted to and breed in overripe fruits, vegetables, and fermenting materials, including those in drains and trash receptacles. They fly slowly, often hovering over food sources.
Assessing the “Harmless” Question: Nuisance vs. Threat
Most common household gnats, like fungus gnats, drain flies, and fruit flies, are primarily a nuisance, not a direct threat to human health. Their presence can be annoying, especially when they swarm around faces, food, or plants. These non-biting gnats lack the mouthparts necessary to puncture human skin.
While most gnats encountered in homes do not bite, specific types, often called “biting midges” or “no-see-ums,” can. These small insects use scissor-like mouthparts to cut the skin, unlike mosquitoes, resulting in itchy, red, and sometimes painful welts. Female biting gnats require a blood meal to produce eggs.
Common household and garden gnats like fungus gnats and drain flies do not transmit diseases to humans. However, some biting gnats, such as sand flies and no-see-ums, are associated with disease transmission in specific regions, particularly in parts of South America where they spread illnesses like Oropouche virus or Carrion’s disease. In the United States, no-see-ums are generally not known to carry human pathogens, though they can transmit diseases to livestock. Eye gnats, attracted to bodily fluids, have been linked to conjunctivitis (pinkeye). Fruit flies can also mechanically transfer bacteria like E. coli and Salmonella to surfaces.
Fungus gnat larvae can damage plants, especially seedlings and young plants, by feeding on their roots. This feeding can lead to stunted growth or wilting. However, adult fungus gnats do not harm plants directly. While gnats can be an annoyance and some types bite, most gnats encountered by the public pose no significant health threat to humans.