Horseflies may be most active in the early morning and late afternoon. You may need to take precautions for you and your horse to avoid being bitten by horseflies. A horsefly is a member of the insect family Tabanidae. They look like small black and red wasps with long slender bodies. There are two species of horsefly that can affect humans: the common horsefly (tabanus bromius) and the so-called European horsefly (tabanus terrestris). The common horsefly is the most common species found in the United States. It's known for its large size and long, slender body. It has a black-and-red pattern on its wings. The common horsefly is often mistaken for the brown dog fly (a member of the order Diptera, or flies). The European horsefly looks similar to the common horsefly. Its legs are a bit shorter and its wings are smaller.