Horse Fly


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Female horse flies in the genus Tabanus bite humans, livestock and wild animals throughout North America. Females need a blood meal in order for their eggs to develop. The males pollinate flowers as they feed on nectar and the larvae are normally aquatic or semi-aquatic.


The horse fly Tabanus stygius will inflict a painful bite. They are very large dark flies found in mid summer bitting during the day. The thorax is whitish with several dark longitudinal lines and the abdomen is black. They often attack both dogs and humans.


The Tabanus larvae are found in moist soil or ponds where they feed on small invertebrates. The adults are strong fliers and search out hosts from a distance.

The painful bite is because the mandibles are sissor-like and cut through the skin. The blood is then sponged up. Small hooks along the edge of the mandibles can help anchor the fly at the site of feeding but also prevents the fly from a quick escape. This means if you can wait for just a few seconds before attempting to swat a feeding horse fly you will have better success.

This fly is a vector of equine infectious anemia also known as swamp fever. This horse disease is transmitted by the bite of the fly. Symptoms in a horse range from fever, anemia up to death. There is a vacine available.


It is difficult to avoid this pest when you are outdoors and the flies are active. They are often found searching on the edge of ponds and open habitats. Females attack relentlessly and are not deterred by the waving of hands.

Artifical traps may work to reduce populations but are of little use when a particluar fly is attempting to bite. You can not out run this fast fly. Instead consider using a fish net to capture and crush the fly. The sticky patches on the back of caps may help some but are untested for this horse fly.

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