Horseflies are building in population here in Southeast Ohio. There are several species of horse flies in Ohio ranging in size from 3/8″ – 1 1/8″ in length. All are aggressive and vicious biters. Horse flies have specialized vision that allows them to see heat; they literally use thermal imaging to locate their hosts. The flies are also able to track large moving objects, particularly dark colored objects, even while the flies are in fast flight. Taken together, their visual acuity allows them to effectively zero in on large, savory, warm blooded animals like cows, deer, people, and of course, horses. Unfortunately for the flies, their visual perception may also cause them to be fooled. A dark colored moving car or tractor that has been warmed by the summer sun looks to a horse fly like a dark, galloping horse, which is why they sometimes chase me when I am on the tractor!
There are a number of things you can do to keep yourself off the horse fly menu. If possible, avoid horse fly habitat. Their larvae feed on decaying organic matter in moist soil, so horse flies are frequently found in swamps or near streams and ponds. If you can’t avoid their habitat, schedule your activities to avoid the flies. Horse flies are active during the day; they can’t find their hosts at night. So, evening pool parties will be free of horse flies. If you must venture into horse fly habitat during the day, remain alert and take precautions. Most flies are silent flyers while horse flies produce a loud, buzzing sound. When you hear the buzz, locate the fly because horse flies love to land stealthily for a quick bite. However, avoid running; remember that horse flies are attracted to moving objects! Wear light clothing. Finally, while insect repellents may provide some protection, horse flies are very good at finding unprotected skin. Long sleeves, long pants, and neckerchiefs can help to thwart the flies.