Home / Pest Library / Flies / Identifying Gnats


  • Colour Black, grey, brown, or yellow
  • Size From 1 mm to 13 mm long
  • Description Have a pair of long wings, spindly legs, and two antennae that exceed the length of their head.
  • Notes Gnats are poor fliers

What do gnats look like

Most gnats are smaller, with less robust bodies, than other species of flies. Ranging in length from 1 to 13 mm, gnats are delicate-looking insects with long wings and spindly legs. Like all insects, the body is divided into three distinct parts: head, thorax and abdomen. The head has a pair of antennae that exceed the length of the head. The pests generally appear black, grey, brown, or even yellow in colour. Fungus gnats have distinct elongated coxae, structures that connect the legs to the thorax.

Habitat, Diet, Lifecycle


Gnats live throughout Canada and the rest of the world. Found in greenhouses, nurseries, and sod farms, certain species of gnats stay close to overwatered and fungi-ridden plants to mate and feed. Other species are found almost exclusively near running water, especially fast-moving rivers and streams.


The dietary habits of gnats vary by species and even by gender. Female black flies, for example, are blood feeders that take blood meals from humans, domesticated pets, and livestock, while males primarily feed on nectar. Fungus gnats, on the other hand, feed on a variety of plants, but the larvae feed mainly on the fungi that grow among overwatered vegetation or in decaying organic matter.

Life Cycle/Reproduction

Like many insects, gnats hatch from eggs as larvae and develop into pupae before emerging as mature adults. Female gnats can lay up to 500 eggs in a lifetime and depend on the presence of moisture to help their offspring mature. Black flies, for example, lay their eggs in running rivers and streams by attaching them in clusters to vegetation and rocks. The emerging larvae likewise attach themselves to plants and rocks by using tiny hooks on their abdomen and pass through six instars while filter-feeding on vegetation in the water. Pupation occurs in silk cocoons underwater, with adults emerging in air bubbles as fully mature gnats.

In contrast, fungus gnat eggs and larvae mature in moist soil, where most of the damage to host plants occurs as the developing larvae feed on organic mulch, leaf mould, grass clippings, compost, root hairs, and fungi. Many types of gnats can produce multiple generations in a single year.

Why do I have gnats

There are more than 600 species of gnat in North America. The most common gnat found inside and around buildings are fungus gnats and dark-winged fungus gnats. Turkey gnats, found outside, are also known as buffalo gnats or black flies.

Fungus gnats like to find overwatered, fungi-ridden plants in greenhouses, nurseries, and sod farms, where they and their larvae can live in moist soil and feed on organic mulch, leaf mould, grass clippings, compost, root hairs, and fungi.

In contrast, black flies prefer running water and lay their eggs on partially submerged objects in fast flowing waters, like streams. The larvae that emerge stay underwater for several weeks, attaching themselves to a rock or branch.

How worried should I be about gnats

Female black flies do bite humans, mammals, or birds to suck their blood to get a “blood meal” required for egg development. This does not transmit disease but can cause a small wound or severe swelling.

However, some tropical species of black flies transmit parasitic nematodes, which cause onchocerciasis, or river blindness, in humans. Additionally, large numbers of black flies attacking an animal all at once can result in death by blood loss or anaphylactic shock.

Fungus gnats can also cause significant damage to and stunt the growth of potted, ornamental and greenhouse plants, as well as crops, when their larvae attack the fungi growing there.

Whatever the species, gnats are extremely persistent and the most effective way of eradicating an infestation is with the help of a professional pest control service.

How can I prevent gnats invading

Avoid overwatering plants, Ensure proper drainage and aeration, Remove standing water promptly, Remove infested soil and vegetation, Seal cracks in the foundations, Fix broken door and window screens.



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