Surprised and irritated by the sudden appearance of numerous small flies? They’re more than likely one of these three most common species: fruit flies, drain flies (a.k.a. moth flies), or fungus gnats. Why should you care about the species? From a scientific control point of view, identifying the species of the invaders ensures effective control. It’s all about the source. Read on to learn about our small fly solutions.

Fruit Flies

Fruit flies on orange

If you have been seeing small flies or ‘gnats’ in and around the kitchen, they are most likely fruit flies. Fruit flies can be a problem year-round but they are especially common in the late summer and fall. This is because they are highly attracted to ripened or fermenting fruits and vegetables. They will also breed in drains, garbage disposals, empty bottles and cans, trash containers, mops, and cleaning rags. All these pests need for development is a moist film of fermenting material. Perishable items from the garden, such as melons, squash, grapes, etc., can be a source of an indoor infestations. Unrefrigerated produce from grocery stores may also be the culprit.

Also known as vinegar flies or pomace flies, fruit flies have played a major role in our understanding of human health. Most of the early research on genetics and genetic-based diseases was done using these flies. Adults are about 1/8 inch long and usually have red eyes but some have dark eyes. The reproductive potential of fruit flies is enormous. Under good conditions, the female can lay up to 500 eggs! Fruit flies undergo complete metamorphosis (change) which includes egg, larva, pupa, and adult. The entire life cycle can be completed in about one week. Fruit flies can pass through standard screening to enter a structure and they are strongly attracted to drains or any location where fermenting liquids are found.

Drain Flies

moth fly drain fly

Drain flies, also known as moth flies or sewer flies, are about 1/8 inch in length, including the wings. They are usually black or grey in color but some appear to be brownish. Adult drain flies are often seen resting on walls near urinals and toilets. They appear somewhat round in overall shape and are not easily disturbed. Moth flies can be serious pests when found in food production/handling facilities and healthcare facilities.

Like fruit flies, drain flies develop by complete metamorphosis. The entire life cycle can be completed in as little as 8 days or up to 24 days, depending on temperature. Adult female drain flies deposit egg masses in the gelatinous film associated with decaying organic matter in drains, garbage disposals, grease traps, sewers, bird feeders and bird baths, gutters, and other places.


Fungus Gnats

fungus gnat

Fungus gnats are also small, usually black flies, with most species being less than 1/16 inch in length. They can be distinguished from fruit flies and drain flies by their long legs.

Fungus gnats are highly attracted to light and may be found flying near windows and around lamps. Larvae are often found in potted plants if the soil is sufficiently moist, where eggs are laid and larvae feed on decaying organic matter. Fungus gnats usually do not harm healthy plants. Although, they may transmit disease-causing organisms from one plant to another. Their presence usually indicates overwatering and insufficient soil aeration.

some dark-winged fungus gnats are stuck on a yellow sticky trap

Yellow sticky cards may be used to control light infestations on indoor plants. Small, raw chunks of potato placed in the soil are very attractive to fungus gnat larvae. These can be used to check for larvae as well as to lure them to the pot surface, away from the plant roots. After a few days, remove the infested chunks, dispose of them, and replace them. Repotting the plant and using sand can also do wonders to prevent a fungus gnat problem.


Small Fly Public Health Importance

Fruit flies, drain flies, and fungus gnats do not bite or sting. They are primarily nuisance pests. However, fruit fly larvae in foods consumed by humans can result in intestinal discomfort and diarrhea. The larvae of some species can also cause human intestinal myiasis, which is an actual infestation of human tissue by the larvae. Because fruit flies and moth flies often originate from filthy sources, they can serve as ‘mechanical vectors’ of human disease, which simply means that they can spread disease-causing bacteria and viruses from filth to food. If you own a food establishment, make sure your pest maintenance program includes small fly elimination. It’s a matter of adding some extra checkpoints to your establishment’s routine visit to make sure employees and patrons stay healthy.

How Do I Find and Control These Small Flies?

Do-It-Yourself methods are not recommended. Pesticides are rarely used to control an infestation of small flies, no matter what kind they are. The best method of eliminating an infestation of these small flies is to find all the actual or potential breeding sources and remove or modify them if possible. Remember that these sources may not always be obvious so you have to look under, over, behind, and within any potential sources. Finding all the sources, correctly determining the type of fly, and knowing the habits of specific species are difficult at best and a Pest Management Professional should be consulted.

The management of food waste and the regular cleaning of floor drains, especially in food-handling facilities, is crucial to preventing/controlling infestations of many types of small flies. Simply pouring bleach or hot water into the drains will NOT eliminate fly larvae that are breeding in the drain’s biofilm. Consult a Pest Management Professional who can then use specific products to treat the drains, kill the biofilm, and thus remove the infestation.

Most infestations of fungus gnats can be traced to overwatering of plants, especially in atriums and other office settings. Simply allowing the plants to dry out completely between waterings will control and prevent the infestation.

If you’re not sure which type of small fly you have, contact us and send us a photo. We’re happy to properly identify it for you and provide a free estimate for a small fly solution. 


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