The term “gnat” is a common, non-scientific umbrella term used to describe many different species of small, non-biting and biting flies belonging to the order Diptera. These insects are often mistaken for one another or for other small household pests due to their minute size. Distinguishing between these tiny flying insects requires observing specific physical characteristics, such as body shape, coloration, and the structure of their wings and antennae.
General Physical Characteristics
Most adult insects broadly categorized as gnats share a delicate, slender body structure. They typically measure between 1/16 and 1/8 of an inch in length, making them some of the smallest flying insects encountered indoors and outdoors. Their overall color is usually dark, often appearing black, dark gray, or deep brown depending on the species and lighting conditions.
A defining feature of many gnat species is their relatively long, spindly legs and a pair of clear or smoky-colored wings. These wings often have a noticeable veined pattern and are held either parallel or in a roof-like position over the body when the insect is at rest. Gnats possess long, thread-like antennae that are segmented and extend beyond the length of their head.
Indoor Gnats: Fungus Gnats and Drain Flies
Two distinct types of flies are most frequently found inside homes and are referred to as indoor gnats, each associated with a different environment. The Fungus Gnat (family Sciaridae) has a slender, mosquito-like appearance with a dark gray to black body. They have noticeably long legs and clear wings that sometimes exhibit a distinctive Y-shaped vein pattern when viewed closely. These gnats are commonly seen hovering around or crawling on the moist soil of houseplants, as their larvae feed on organic matter and fungi within the potting mix.
Drain Flies, also known as moth flies (Psychodidae), look completely different, having a distinctly fuzzy or hairy body and wings. Their dense hair covering gives them a moth-like silhouette, and their wings are typically held in a characteristic roof-like posture over their body when they land. These flies are often light gray or tan with darker wing edges and are found resting near sink drains, showers, or any area with standing water and organic sludge buildup.
Outdoor Gnats: The Biting Varieties
Gnats encountered outdoors, particularly the biting varieties, have unique physical features reflecting their different biological families. Biting Midges (Ceratopogonidae), commonly called “no-see-ums,” are exceptionally tiny, often measuring less than 1/16 of an inch long, making their size the primary identification feature. They are gray-black and are easily missed until their presence is confirmed by a bite, since their minute size allows them to pass through standard window screening.
Black Flies (Simuliidae) present a different profile, being stockier and noticeably humpbacked, which gives them the nickname “buffalo gnat”. These flies are dark in color, typically black or brown, and are slightly larger than midges, measuring about two to four millimeters in length. The Black Fly has broad, clear wings and is usually found near fast-flowing water where they breed.
Distinguishing Gnats from Similar Small Pests
Fruit Flies (Drosophilidae) are often confused with Fungus Gnats, but they possess a rounder, more robust body shape that is tan or brown, unlike the slender, dark body of a gnat. The most defining characteristic of the common Fruit Fly is its bright red eyes, which are easily visible, in contrast to the small, dark eyes of most gnats. Fruit Fly antennae are short and stubby, a visual difference from the long, segmented, thread-like antennae that gnats possess.
Distinguishing gnats from Mosquitoes (Culicidae) involves noting the absence of a long, needle-like proboscis on the gnat, a structure mosquitoes use for piercing skin and feeding. Mosquitoes are also generally larger than gnats and have scales covering their wings and bodies, features not found on a gnat. House Flies (Muscidae) are significantly larger, typically measuring 1/4 inch or more, and have a distinctive gray body with four dark stripes on the thorax.