There are many types of biting insects that seek horse blood. According to the Merck Veterinary Manual, the most common are: Mosquitoes: These have been described as “the most voracious of the blood-feeding insects.” These tiny, buzzing creatures often make stagnant water their breeding grounds, laying their eggs on the surface, which is why swampy conditions are riddled with mosquitoes. Mosquitoes are especially dangerous to horses because they can transmit viral encephalitides (brain inflammatory diseases), including Western and Eastern equine encephalomyelitis (WEE/EEE) and West Nile virus (WNV). Biting midges: Also called gnats and no-see-ums, these tiny, gray, two-winged flies live in wet soil. They deliver painful bites and suck blood, and many horses develop allergies to their saliva, making them the main culprits in insect bite hypersensitivity (read on to learn more about this condition). Stable flies: These are blood-feeding insects known for pestering animals and humans alike. They look like house flies—picture your typical black fly—but slightly smaller, and they bite! Stable flies exist throughout the world; in the US, they are found mainly in the Midwestern and Southeastern states. Horseflies: These are the largest beasts on this list, some longer than an inch. Their bites are painful and draw blood, creating oozing wounds. Aptly named, these black insects with gray wings (although coloration can vary) feed off horse blood and are the hardest to kill with traditional fly repellents. Larvae develop in aquatic to semi-aquatic areas, making horseflies more prevalent in tropical climates. Horseflies are especially dangerous because they can transmit diseases, such as anaplasmosis and equine infectious anemia (EIA).,Jump to section 4 Types of Insects That Bite Horses Top 3 Risks of Fly Bites on Horses Symptoms of Fly Bites on Horses Treatment of Fly Bites on Horses Prevention of Insect Bites on Horses FAQs About Fly Bites on Horses