Gnats: What to Know

Medically Reviewed by Jabeen Begum, MD on January 02, 2024
9 min read

Gnats are annoying little critters. They can get in your face, nip at your skin, and annoy livestock. They can also damage your household plants. There are many species of gnats, and though they all look similar, they may have very different habits.

Gnats are a group of tiny, winged flies. They belong to the fly order Diptera, which includes mosquitoes, flies, and maggots. You may also hear them called biting midges or blackflies, among other names.

What do gnats look like? There are many species of gnat, but most of them look very similar and are hard to tell apart. Characteristics include:

  • Gnats are very small, usually between 1/16 and 1/8 of an inch long. 
  • They have slender black bodies.
  • Gnat wings are translucent with veining, and they usually fold their wings behind their back when not flying. 
  • Gnats have six legs and antennae. The antennae are usually a moderate length.

What do gnats eat? A gnat's diet will depend on what species it is and what stage of its life cycle it’s in. Gnats have been known to eat algae, decaying plant matter, fungi, nectar, and plant roots. For some species, the female requires a blood meal in order to lay eggs. 

Gnats vs. fruit flies

Fruit flies are also Diptera but look, act, and eat slightly differently than gnats. Fruit flies:

  • Are brownish or orange
  • Have round lower bodies
  • Fly slowly, usually just hovering over their food
  • Eat the yeast found on rotting produce or decaying plants and animals

Gnats go through four stages in their lives: egg, larva, pupa, and adult. The exact reproductive habits and life cycle depend on the species. 


Female gnats lay their eggs in the environment their species prefers to feed. This could be in soil, in water, or on plants. Female gnats can lay hundreds of eggs. Eggs can range in color, depending on the species, and may be shades of white, yellow, or orange. The eggs can hatch quickly, sometimes in less than a week. 


When gnat eggs hatch, they produce larvae, which look like worms and don't have heads, wings, eyes, or a visible head. They have two hooks in their mouth that are used to bite and chew. Some species have more than one larval stage. For some species, they larvae overwinter, finishing their life cycle in the spring.


Depending on the species, gnats may stay in their pupal stage for a few days or a few weeks. During this stage, they are encased in a cocoon. When the pupal stage is complete, they come out as a full adult gnat. 


Gnats have two sets of wings. ("Diptera" means "two wings.") The front set are used to fly, and the hind wings are tiny and club-like, known as halteres. Gnats are a suborder of Diptera known as Nematocera. This group has long legs and antennae and look fragile. 

How long do gnats live? 

Once they reach the adult stage, gnats generally only live about 7-10 days. The entire lifespan of a gnat – without overwintering – can take 3-4 weeks, depending on the species.

There are many species of gnats, each with its own habitat, life cycle, and diet. 

Fungus gnats. Fungus gnats are a common type of indoor pest that like to feed on houseplants. They’re sometimes mistaken for their equally small cousin, the fruit fly. An up-close look will help you tell the difference, as fruit flies have light-colored bodies and red eyes.

Female fungus gnats lay their eggs in potting soil or other types of moist organic debris. The larvae are about a quarter of an inch long and have a dark head. The larvae are the biggest problem for people because they can feed on plant roots if their preferred food of algae and fungus runs out. 

Fungus gnats do not bite, but they can be a nuisance. They often fly around the heads of people and animals, feeding off of mucus released from eyes, ears, and other areas. 

Biting gnats. In species of biting gnats, female gnats must have a blood meal in order to lay their eggs. These types of gnats often lay their eggs in sources of running water, either directly into the water or onto plants trailing in the water. Some species may also lay eggs in moss, potholes, soil, and tree bark.

When these gnats bite, they don’t do it the way a mosquito does. Mosquitoes have needle-like mouth parts that they use to pierce skin, while gnats use scissor-like jaws to cut open the skin. Their saliva can cause an allergic reaction, which for most people is usually mild. They can’t bite through fabric, so they only affect exposed skin. They usually feed in the morning and evening. 

Fungus gnats are typically harmless to humans because they don't bite. They can spread diseases like:

  • Pinkeye (when they are in one eye that is infected and then land in another)

  • Sepsis between people (when your body has an infection and your immune system overreacts, causing inflammation throughout the body)

  • Mastitis among cattle (an infection in the breast that causes inflammation)

The main issue you will have with fungus gnats is with your plants. Once their population has increased and gotten into your houseplants, their feeding habits can cause yellowing and stunted plant growth. 

More specifically, fungus gnat larvae can be dangerous for your young or weak plants because they deplete the plants of the nutrients they need to thrive, remove root hairs, and may even tunnel into the root itself. Fungus gnats can also spread pythium, which is a plant pathogen that causes damping off, a condition that can rot the roots of seedlings, making them die.

Biting gnats don't transmit diseases between humans. If you get bitten, you may have a small welt at the site and some itching that can be intense. They do transit a condition called blue tongue virus to livestock in North America.

Fungus gnats are found throughout the United States and on other continents. They are usually found where there are plants and moisture. These pests are most noticed during late fall and winter, mostly due to plants being brought indoors, out of cold weather. Gnats that were on the plants outside are brought in. Also, because days are shorter and indoor temperatures may be cool, the soil stays moist longer, making it more attractive for gnats. 

Fungus gnats are found in different areas of the plant, depending on where they are in their life cycle. The eggs are laid in the plants' soil. As larvae, gnats remain within the soil, feeding on the plant roots, fungi, and organic matter. The pupae then emerge from the soil, where they reside for 4-6 days before beginning their adult stage and flying around the plant for the remainder of their life.

Although less common, fungus gnats can also be found in drains. Drains are moist areas that, over time, grow organic matter. This makes them the perfect breeding ground for fungus gnats. Without proper cleaning of your drains and removal of the infestation, fungus gnats can continue to have a presence in your sinks and toilets.

Gnats don't fly well, so they usually stay near the plant or sink where they developed. Sometimes, though, you can find them around nearby windows, as they are attracted to light. Biting gnats are also found around plants because their main food source (except when females are producing eggs) is sap and plant nectar.

Like mosquitoes and fruit flies, gnats aren’t sneaky. You’ll know you have them because you’ll see them. 

Gnats in houseplants

Fungus gnats will be hanging out on or near plants. If you’re having a hard time telling gnats from other insects, you can place a sticky card near the plant to trap adults or put a slice of potato on the surface of the soil to draw out larvae. 

Outdoors, gnats are generally most active during the midmorning and at dusk. They’re attracted to light and may swarm lampposts or porch lights. 

Biting gnats

Another sign that you have gnats is gnat bites. These typically appear on exposed areas of the body like ears, eyes, noses, and wrists. Symptoms of gnat bites include itching, pain, and localized swelling.

Houseplants attract fungus gnats, especially if the soil is retaining a lot of moisture or holds decaying plant matter.

Outdoors, gnats are a part of nature. While wet areas and areas of standing water may attract them, there isn’t always something specific that is causing gnats to infest your area. 

If you get bitten by a gnat, wash the area thoroughly with soap and water. Apply some antiseptic as well. Anti-itch cream and ice packs can help reduce itching and swelling.

To avoid gnat bites, apply a DEET-based insect repellent before going outside. Wear long-sleeved shirts and long pants when going hiking, especially near streams and rivers. Gnats can't bite through clothing, so you can only get bitten on exposed skin.

If you have gnats in your home, or want to avoid them outside, there are some things to do to keep them away.

How to get rid of fungus gnats in plants

Soil maintenance. Let the soil get as dry as you can without your plants wilting. Repot your plants when the soil starts to hold too much moisture or if the soil becomes full of decaying matter. Use pesticides in the case of a large infestation. Bacillus thuringiensis, subspecies israelensis, strain AM 65-52 will kill larvae. After the pesticide kills the larvae, wash off your plant's roots and repot it in a clean container with fresh soil.

Sticky traps. Sticky traps are a great way to monitor your fungus gnat population and make sure fewer survive. They can be stuck into the soil of the affected plant. The fungus gnats will get stuck to the traps when they fly around, preventing them from further breeding.

Cider vinegar traps. Cider vinegar traps are an easy at-home management strategy. To make one, fill a shallow container with a small amount of apple cider vinegar, water, and liquid dish soap. The gnats will be attracted to the cider vinegar and get stuck in the mixture due to the dish soap.

Regularly clean your drains. Because drains are an ideal breeding ground for fungus gnats, it's important to rid them of the organic matter that helps gnats thrive. Regularly cleaning your drains will ensure that organic matter doesn't grow there. Although the drain may remain moist with continuous use, the organic matter is what allows the fungus gnats to grow and breed.

A proper management system can help get rid of these pests and avoid their presence in the future. If you're having a difficult time managing these pests on your own, you can reach out to a pest control professional for more tips and tricks.

How to get rid of gnats outside

Outdoors, there isn’t much you can do to prevent gnats. Some pesticides work, but usually only short-term. You can also try to remove areas of standing water, like birdbaths or buckets. To keep them out of your home or enclosed patio, install screens with small mesh – traditional 16-mesh screens are too big. Running a ceiling fan on high speed can also knock these bad flyers out of your space. If you are planning outdoor activities where there may be biting gnats, try to avoid being out around dawn and dusk, when they are the most active. 

Gnat repellents

DEET (N,N-diethyl-meta-toluamide) may help repel gnats for 2-8 hours. There are a number of products with different concentrations of DEET, but anything over 30% could irritate your skin and eyes. 

Picaridin is also a gnat repellent than may be gentler on the skin than DEET.

Oil of lemon eucalyptus is a plant-based gnat repellent that is safe for people over the age of 3 to use. It is about as effective as DEET, but it doesn't last as long. Don't use this product around your eyes, because it can irritate them.