Horsefly bites are lesions caused by bites of horseflies.


Horsefly adults can be as small as housefly and as large as 4cm in length, yellowish brown, gray, or black.

Horsefly has piercing-sucking mouthpart and strong flight force. Females lay eggs on the grass blades and stones in the paddy fields, swamps, lakes, and ponds. The eggs are hatched into larvae in about 1 week. The larvae fall into the water and feed on mosquito larvae. The grown-up larvae can also feed on molluscs such as earthworms. After maturing, they develop into pupae in the soil in October, and they escape from the pupae and develop into adults in May of next year.

The males have degenerated mouthparts and do not suck blood, and feed on plant sap. Female horseflies mainly suck blood from the cattle, horses, and donkeys, and sometimes invade other animals and humans. Adults like the daytime and are active under the scorching sun, and usually suck blood at noon. The amount of blood sucked can be 3 - 4 times the body weight of horsefly. Multiple or continuous bites can cause the transmission of blood-borne diseases. The deerflies in Africa is the vector of loiasis, and the deerflies in North America and Russia can transmit rabbit fever.

Signs and Symptoms

There are immediate, severe pain after bites, and obvious redness and swelling occur on the skin, with traces of bites in the center. There may be hemorrhage as horseflies secrete anticoagulant substances during bites. Horsefly larvae can bite the skin when humans work in the water, and there may be severe pruritus, sharp pain, redness, swelling, papules, and wheals.


If there are horseflies and clinical manifestations, the disease can be diagnosed.


Topical calamine lotion can be used, and compression may be necessary to prevent from bleeding.