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Large Flies

You’ve Seen Large Flies in your House – What Could They Be?

When home and business owners think of flies, the most common species associated with households would be the house fly. Though the house fly remains one of the predominant insect pests in Canada, there are other large flies found in Canada, some of which include horse flies, deer flies, blow flies, flesh flies, and crane flies. Flies such as the horse and deer fly pose health risks to livestock, pets, and humans alike by being annoying and carrying various pathogens.

Deer Flies & Horse Flies

The deer fly, Chrysops species, and the horse fly, Tabanus species, both also referred to as tabanids, are stout-bodied, fairly large flies, ranging in size from 6 to 32 mm. Body colour varies from black, gray, yellow, purple, to green depending on species. Deer flies and horse flies are easily identified by the relatively very large, brilliant, iridescent coloured compound eyes, which touch each other in males, and fairly prominent mouthparts adapted for biting and sucking. Both sexes of deer flies and horse flies feed on sugar obtained from flower nectars for their energy needs; however, the females attack and feed on the blood of larger mammals including humans. The blood is needed for egg development. Host preference and feeding behaviour varies depending on species of the fly, though as the names suggest, the deer fly mainly attacks deer and the horse fly primarily attacks horses, although they both will attack other animals, too. Both deer flies and horse flies are strong fliers and can easily disperse over long distances. In Canada tabanids are more of a nuisance because of their painful bites. The pests are less likely to transmit pathogens compared to the tropics. However, they are also known to transmit several pathogenic viruses, bacteria, and parasites that cause diseases in humans, livestock and wild animals.

Crane Flies

Crane flies are another group of fairly large flies with body size ranging from 15 mm to 25 mm long. They look like mosquitoes, except for their long, thin bodies and extremely long legs, which often break off easily. Crane flies do not have biting mouthparts; therefore, they do not bite humans or other animals. The insects typically breed outdoors in moist environments that have lots of vegetation or plant material on which the larvae feed. Crane flies are attracted to light, and occasionally they will enter into buildings when doors or windows are left open and can become a nuisance. However, crane flies do not survive well indoors, so they often die shortly after entry. The European crane fly is a major pest of turfs, pasture grass, and field crops in Canada. Damage is caused by the larvae, often referred to as leatherjackets.

Blow Flies

The blow fly, Calliphoridae, appears a shiny blue, green, bronze, or black colour and may reach lengths up to 14 mm. Blow flies display typical fly behaviours; the larvae feed on carrion or other decaying organic matter. At times, the larvae may infest the wounds on cattle and can cause problems for humans as failure to identify the larvae may lead to infections of the blood. Large numbers of blow flies in a home or business may be indicative of the presence of a dead animal, large amounts of trash, or a break in a sewage line. As with most insects, a proliferation of any fly species needs addressed as soon as possible. In order to effectively eradicate a large fly problem, contact a trained pest control expert.