Do Gnats Bite? Which Gnats Bite and How to Stop Them

Do gnats bite? Some do and some never do. Biting midges (also called no-see-ums or sand gnats) and black flies bite, and only the females, because they need a blood meal to make eggs. Fungus gnats around houseplants and eye gnats do not bite. A midge bite looks a lot like a small mosquito bite.

"Gnat" is a nickname for several tiny flies. Once you know which one is around you, you know the fix, and you can get back to the porch, the trail or the dock.

Do gnats bite? The short answer

Clemson Extension says "There are two different small flies that are referred to as gnats", and they "differ greatly in habit as well as the way they interact with humans." Add the black fly (a biting gnat to Minnesota's Metropolitan Mosquito Control District) and the houseplant fungus gnat, and you have four:

• Biting midges (no-see-ums, sand gnats): bite. Females only.
• Black flies: bite. Females only.
• Eye gnats: do not bite.
• Fungus gnats: do not bite.

In both biting groups, males feed on nectar and only females take blood, to develop their eggs.

Which gnats bite (and which never do)

Biting midges, also called no-see-ums

Clemson Extension says: "Biting gnats, also called sand gnats or no-see-ums, are in fact biting midges." They are tiny, around 1/16 inch by Clemson's measure, which is why most people never see one feed and why they earned the name no-see-um. Females feed mostly early and late in the day.

They live near water: swamps, marshes, ponds and stream edges (Clemson), plus coastal salt marsh and mangroves (UF/IFAS). For more, see our guide to what no-see-ums are.

Black flies

Black flies are closely related to mosquitoes, according to Minnesota's Metropolitan Mosquito Control District. Female black flies take blood to develop eggs, and males do not bite. Females are an eighth to a quarter of an inch long. They breed in rapidly flowing water such as streams and rivers, and the district monitors adults from May to September.

Eye gnats

Clemson Extension is clear: "eye gnats do not bite." Also called grass flies, eye flies or frit flies, they are about 1/8 inch long and swarm around the heads of people and animals, feeding on mucus from the eyes, nose and ears. They are a nuisance, most common where soil is loose, sandy and disturbed.

Fungus gnats

University of California IPM describes fungus gnats as small nuisance flies that commonly turn up in potted plants. Their larvae feed on fungi and organic matter in the soil. The adults are dark, delicate and look similar to mosquitoes, at about 1/16 to 1/8 inch. The good news, in UC IPM's words: "Adult fungus gnats don't damage plants or bite people; their presence is primarily considered a nuisance."

Which gnat is it?

The four side by side, each detail from an extension or district source.

What do gnat bites look like?

It depends on the gnat. A biting midge leaves "an itchy, raised spot on their victim's skin very similar in appearance to a mosquito bite," per Clemson Extension, often without you ever seeing the insect.

A black fly bite is different. Minnesota's Metropolitan Mosquito Control District says: "The painful, itchy bite of the black fly is characterized by a reddened weal with a wound in the center." The female cuts a small hole in the skin to feed.

For a closer look at midge bites, read our post on what no-see-um bites look like.

Gnat bites vs mosquito bites

A midge bite and a mosquito bite can look almost the same. Three clues help:

• Time of day. As the Minnesota district puts it, "unlike mosquitoes, black flies are daytime feeders."
• What you saw. Saw nothing? Think midge. University of Arizona Extension says no-see-ums are barely visible and look like miniature mosquitoes up close.
• Where you were. A marsh or the coast at dusk points to midges; a fast stream on a sunny day points to black flies.

If the real question is bites that appear overnight, see our guide to bites that show up overnight.

When and where gnats bite

Biting midges keep to the edges of the day. Clemson Extension says females feed mostly early and late in the day, University of Arizona Extension says dawn or dusk, and UF/IFAS adds daytime on cloudy, calm days. They stay close to marshes, ponds, stream edges and coastal salt marsh.

Arizona Extension says midges peak in summer, but in places with warm winters they can occur year-round. Black flies feed in daytime near running water, and the Minnesota district monitors them from May to September.

And the part we like best this time of year: Clemson Extension, writing about South Carolina, says: "The first killing frost in the fall is always a welcome relief."

Can gnats bite you in bed or indoors?

The gnats you most often see indoors are fungus gnats, and they do not bite. UC IPM says they stay near potted plants, are attracted to light and are often noticed near windows.

No-see-ums are the exception worth knowing. University of Arizona Extension says standard 16 x 16 or 18 x 16 window screen lets them through, while 30 x 30 mesh keeps them out, and that they occasionally bite people indoors. UF/IFAS adds that biting midges "do not establish inside homes," so an indoor bite usually means one drifted in from outside.

If bites keep showing up in bed, gnats may not be the answer; the 30-second check below points you to the next step.

The little gnats in your kitchen this winter

Tiny flies near the houseplants in November? Those are most likely fungus gnats, and they do not bite. UC IPM says they can turn up indoors any time of year, and they thrive in moist conditions. The fix is low effort:

• Avoid overwatering and give pots good drainage.
• Let the surface of the soil dry between waterings.
• Clean up standing water in saucers.
• Use yellow sticky traps to catch adults.

UC IPM notes that insecticides are generally not recommended for fungus gnats around the home. Dry soil does most of the work.

Where were you when it bit? A 30-second check

• Indoors, near houseplants, no bites: fungus gnats. They do not bite. If you are finding bites, look for another cause, starting with our bed bug vs mosquito bite guide.
• At dusk, near a marsh, beach or soggy lawn, and you never saw the bug: biting midges. Start with our no-see-ums guide.
• In daytime, near a fast stream or river in spring or summer: black flies.
• Swarming your eyes and face, but no bites: eye gnats.

Know the gnat, know the fix, and the evening is about the view again.

How to keep biting gnats off you outside

Dress for it. Minnesota's Metropolitan Mosquito Control District recommends light colored clothing, since black flies are attracted to dark colors, plus long sleeves, pants and a hat, because "black flies don't bite through clothing." For midges, University of Arizona Extension adds socks and a hat with fine mesh netting.

Time it. Plan around peak biting times: daylight for black flies, dawn and dusk for midges.

Screen and fan the porch. Clemson Extension recommends very fine mesh, 20 x 20 or smaller, to keep biting midges off a screened porch. A ceiling fan under a covered porch or a box fan helps too, since gnats are small enough to be blown off course.

Use a repellent, and follow the label. The Minnesota district lists repellents such as DEET, picaridin or oil of lemon eucalyptus (OLE) for black flies, and a head net where they swarm. University of Arizona Extension says: "Repellents effective against mosquitos are effective against biting midges." For mosquitoes, the CDC lists these active ingredients for EPA-registered repellents: DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol (PMD) and 2-undecanone. The CDC describes OLE and 2-undecanone as plant-derived, and says: "Always follow label instructions." For sprays in midge country, see our post on which spray to use for no-see-ums.

Our pick for porch and dock evenings

My co-founder and formulator Cassidy Huang and I spent two years working with a Taiwan-based chemist to develop Bloc Off Spray. It uses 8% plant-based PMD (para-menthane-3,8-diol) derived from lemon eucalyptus, and it is lab-tested for 6+ hours of protection against mosquitoes, ticks and other biting insects. We make no gnat, midge or black fly claim for it.

It is DEET-free and alcohol-free, with aloe vera, chamomile and shiso (perilla) for a clean herbal note. A 4 oz (118 ml) bottle is $15.00, and Bloc Off Wipes come as 10 individually wrapped wipes for $13.00. Add long sleeves, a porch fan and good timing, and the golden hour is yours again.

FAQ

Do fungus gnats bite?

No. University of California IPM says: "Adult fungus gnats don't damage plants or bite people; their presence is primarily considered a nuisance." Letting the soil surface dry between waterings is the main fix.

Can gnats bite you in your sleep?

Indoor gnats are usually fungus gnats, which do not bite. No-see-ums can slip through standard window screen and occasionally bite indoors (University of Arizona Extension) but do not establish inside homes (UF/IFAS). If bites keep appearing in bed, see our bed bug vs mosquito bite guide.

Why are gnats biting me?

Usually it is place and time. Midges stay near marshes, ponds and stream edges and feed early and late in the day; black flies feed in daytime near fast water. Near their breeding water at their biting hour, you are in their zone.

What smell do gnats hate?

None of the extension sources we used recommend a scent. They recommend fine mesh, fans, light long sleeves, timing, repellents used per the label and, for fungus gnats, drier soil.

Are no-see-ums gnats?

Yes, in everyday language. Clemson Extension says: "Biting gnats, also called sand gnats or no-see-ums, are in fact biting midges." Our no-see-ums guide covers them in detail.

Written by Tanya Lee, Co-Founder of The Superbloc. Sources: Clemson Cooperative Extension HGIC 2489 "Gnats"; Metropolitan Mosquito Control District (Minnesota), "Biting Gnat/Black Fly Control"; UC Statewide IPM Program, Pest Notes "Fungus Gnats"; University of Arizona Extension, "Something's biting me, but I can't see it!"; UF/IFAS EENY 349; CDC, "Preventing Mosquito Bites."