Horse flies are often confused with regular flies – at least until they bite. It is usually at this point when the victim realize this is no ordinary fly bite.

The horse fly should really be named the vampire fly. It is a voracious feeder, and a swarm of females can relieve its victims of as much as 2 cups (1 pint) of blood in less than one day.

Like another much-loathed pest, the mosquito, the horse fly requires a body of water to breed. The females also require a blood meal before they can make baby horse flies.

Since bodies of water and large warm-blooded mammals like horses and cattle are commonly found near one another, the horse fly tends to gravitate to breeding grounds that offer both. This well-documented behavior is how it got its name.

How a Horse Fly Eats

While they look fairly small as they fly around, these biting insects actually have ferocious mandibles (jaws). So rather than politely inserting a tiny sucking straw when they want to dine, the horse fly will rip and tear at the skin with her giant jagged jaws. She will then lap up the blood similar to how a dog might lap up water.

This explains both why horse fly bites are so painful and why they are considered a vector (carrier) for many infectious diseases, most notably swamp fever, aka Equine Infectious Anemia (EIA). Equines and related species that develop EIA lose weight and energy until they are successfully treated or die of the disease.

Fending Off a Horse Fly

Some biting insects, such as mosquitoes, are really rather fragile. As such, a single well-placed swat is likely to achieve a cease and desist. This is not the case with the robust and hardy horse fly, however. A horse fly may pursue its chosen prey for many miles without ceasing.

It is generally quite difficult to fend off hungry flies, since they don’t respond to insect repellants, even ones that contain powerful chemicals like DEET.

The best way to minimize the risk of being bitten is to stay indoors, since these insects prefer to remain outdoors. Wearing heavy clothing and protective hats can make it more difficult (although not impossible) for a horse fly to bite.

The hands-down best way to achieve horse fly prevention is to eliminate bodies of water that can serve as breeding areas or to kill the flies while they are in the larval stage.

Contact YES Pest Pros

YES Pest Pros has developed an eco-friendly, integrated approach to horse fly management. This system includes the use of green pest management substances, mechanical traps, inspection to eliminate breeding sites and sanitation of those areas and exclusion to keep more flies from entering the area. To learn more, visit