Learn to recognize and understand the top four insects that can put the “bite” on your horse – and on you!

They may be small, but there are insects out there that can affect the health and comfort of your horse – and even your safety as a rider. Can you recognize these insects and the symptoms of their bites or stings, and do you know how to manage them safely and effectively?

The Hit List

Let’s start with a quick review of the blood feeders. Most of these groups have representative species in every region of the country. The importance of each can vary by location, and even from year to year based on weather patterns. Their bites are often painful, and some are potential disease vectors. While it may take many bites to bother a horse, a single bite from an infected insect can transfer a pathogen that may result in illness, debilitation, or in some cases even death.

1 Mosquitoes (Family Culicidae) are at the top of the list. Some species are vectors of encephalitis (Eastern Equine, St Louis, and West Nile), while others are just an annoyance. Some can be a problem during wet years, while others thrive under dry conditions. Excessive spring rains over much of the country this year led to large populations of floodwater mosquitoes. The eggs of these mosquitoes can survive for years in low-lying areas, hatching quickly when covered by pooled water. While floodwater mosquitoes are generally not disease vectors, huge numbers can develop quickly and move up to ten or 20 miles as they disperse and search for blood meals. Because of this, there is no opportunity to deal with breeding sites – a key strategy in mosquito management. The best way to protect horses is to keep them inside during prime feeding times for mosquitoes, or apply protectant insecticide applications or sprays. Fortunately, floodwater mosquitoes tend to be active for only a relatively short period.

Several mosquito species breed in the green water that accumulates in artificial containers. Reduced rainfall results in a small number of sites, but the abundant microbes in the “dirty” water provide food for mosquito larvae (wrigglers). Several of these species feed on birds and mammals, providing a bridge to move the encephalitis virus to horses or humans. These mosquitoes stay near the breeding sites, so riders can help manage mosquitoes locally by eliminating or treating standing or collected

2 Horse Flies and Deer Flies (Family Tabanidae) are persistent, painful biters that attack horses and riders during the day. These flies use their excellent eyesight and strong flying ability to dart to hosts from resting sites on vegetation. Blade-like mouthparts slice the skin, creating small pools of blood for the flies to take up. These noisy insects can make horses difficult to handle as the animals try to stop or escape the incessant bites. The flies’ blood meals are often interrupted by defensive actions from the horse – consequently, a fly may have to visit several animals in order to get a complete meal. This pattern of interrupted feeding increases the chances of disease transmission.

Tabanids are very signifcant vectors of equine infectious anemia in some parts of the US. Tabanid larva are semi-aquatic – they develop in soils along creek banks, seepage areas, or other moist sites. This means there is no practical means of controlling breeding sites. Protection must be focused on the animal. Insecticides or sprays may provide some temporary relief from bites, but flies must land on the treated coat to come in contact with the product. They may land and attempt to bite before the product has a chance to work. Horses are bothered even if the flies don’t feed; protective applications appear to be ineffective.

3 Ticks, relatives of insects, are particularly troublesome for horses that are pastured or ridden in overgrown brushy areas that provide the protection and small animal hosts needed for blood meals. Hungry ticks wait on vegetation along trails and the margins of wooded areas with their front legs extended to cling to passersby. They move upward in search of a suitable feeding site and insert their barbed mouthparts. A cement-like substance holds them in place until they are engorged. Then they detach and fall to the ground.

Tick numbers are generally lowest in open, sunlit areas with scarce or short vegetation. They soon perish in hot, dry areas. In some cases, it may be possible to ride in areas that are not obvious “tick country”.

However, that is often just not practical, so regular tick checks allow you to detect and remove the pests, hopefully before they have a chance to attach. Check protected areas where the hair coat is thin, especially along the mane and around the tail head. Embedded ticks should be removed carefully. Grasp them with tweezers as close to the skin as possible and pull slowly and steadily until they detach. A thorough grooming after the ride can help locate ticks that were missed.

4 Stable Flies may be last on this list but they could also be right at the top, especially based on their painful bite. Stable flies usually feed once a day, preferring to land on the lower leg or along the belly of the horse. Horses bothered by stable flies frequently stomp their feet in an attempt to stop the relentless attack. As with horse and deer flies, this results in interrupted feedings. Stable flies can be vectors of equine infectious anemia.

Stable flies breed in decaying feed, vegetation, and hay or straw mixed with feces or manure, so they can be abundant around stables and barns. The life cycle from egg to adult can be as short as three weeks, so regular sanitation and waste management around your facility can play a major role in managing this insect.

As large mammals, horses present attractive targets to many blood-feeding arthropods. It is difficult to protect them when pest populations or the threat of disease are high. Knowing the behavior and activity patterns of insects, along with management practices and potential protectants, can help maintain a comfortable and healthy horse that can be handled safely.

Lee Townsend is an extension entomologist in the UK College of Agriculture. He is responsible for extension programs with livestock, forage, and tobacco insects and is coordinator of the Kentucky Pesticide Safety Education Program.