Deer flies are a little larger than a housefly and are stout-bodied. They are colored yellow or black and have dark colored markings on their wings. Their eyes are often a brightly colored green or gold pattern. Deer fly larvae live in aquatic or semi aquatic sites, like marshy areas, streams and ponds. Adults are found near these breeding grounds, especially along the edges of woodlands but they are strong fliers and can range miles away from their breeding areas. They are most active on sunny, calm days and have a tendency to wait in shady areas for a host. Deer flies primarily use sight to find a host and seem to be particularly attracted to moving, dark shapes. They typically go for the head and neck when biting people. They can inflict a painful bite as they seek a blood meal causing an allergic reaction in some people. They use knife-like mouthparts to slice a wound in the skin and feed on the resulting blood. Deer flies are most common in June and July, although they do persist until the end of summer.