Deer flies (also known as yellow flies, or stouts in Atlantic Canada) are flies in the genus Chrysops of the family Tabanidae that can be pests to cattle, horses, and humans. A distinguishing characteristic of a deer fly is patterned gold or green eyes. The name of the genus refers to their coloration, from the Ancient Greek χρυσός (chrysós), gold, and ὤψ (ops), appearance.
Deer flies are a genus of horse-flies (Tabanidae). They are smaller than wasps, and have coloured eyes and dark bands across their wings. While female deer flies feed on blood, males instead collect pollen. When feeding, females use knife-like mandibles and maxillae to make a cross-shaped incision and then lap up the blood. Their bite can be painful, but many bites are not noticed at the time, especially if the victim is distracted. Allergic reaction from the saliva of the fly can result in further discomfort and health concerns. Pain and itch are the most common symptoms, but more significant allergic reactions can develop.
They are often found in damp environments, such as wetlands, bogs, or forests. They lay clusters of shiny black eggs on the leaves of small plants by water. The aquatic larvae feed on small insects and pupate in the mud at the edge of the water. Adults are potential vectors of tularemia, anthrax and loa loa filariasis.
Predators of the deer fly (and other Tabanidae) include nest-building wasps and hornets, dragonflies, and some birds including the killdeer.
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