- 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
Often mistaken for mosquitoes, gnats are “true flies” and belong to the order Diptera. The relatively small insects are usually poor fliers and infest residences as well as commercial and industrial sites. There are over 600 species of gnats found in North America. The most common species found inside and around buildings are fungus gnats and dark-winged fungus gnats. They can be a nuisance or cause significant damage to ornamental plants and garden crops, while some species such as the buffalo or turkey gnat, also known as the black fly, attack humans and other animals to feed on blood.
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.
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.
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.
Problems Caused by Gnats
Generally a nuisance pest, adult gnats become active and swarm during the warmer months. Certain species can directly affect the growth of potted, ornamental, and greenhouse plants. When plants become overwatered and the soil is not allowed to dry properly, larvae may attack the fungus that ends up growing, resulting in damage and stunting the growth of the plant.
Other species, such as the buffalo gnat, may actively attack humans, pets, and livestock to feed on their blood. Though most North American species of gnats are not known carriers of diseases, 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.
Detection/Signs of Infestation
The surest sign of infestation is the sight of adult gnats flying around. In particular, the presence of large populations of swarming gnats usually indicates an incursion problem. Noticing damaged plants near ground level and seeing larvae in the soil also clearly signifies a gnat infestation.
Exclusion represents the most effective form of prevention. Avoid overwatering plants to reduce fungus gnat populations and breeding grounds, and get rid of currently infested soil and vegetation. Application of appropriately labelled insecticides in affected areas may help prevent infestations of black flies or other gnat species that commonly travel great distances to locate food sources.
Most gnats are attracted to light, the use of light traps can be effective in controlling gnat populations. For black flies, wearing light colours and long sleeves will help keep the pests at bay. Since gnats are so persistent, controlling the insects at the larval stage of the life cycle proves to be the most effective. Finding and eliminating breeding conditions and sites is the most effective long-term control method. It may be necessary to contact a trained pest management professional for the complete control and management of gnat infestations.
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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