Horse Flies

Horse-fly (Tabanidae – insect order Diptera).

Horse-flies are often large and agile in flight, and a nuisance to animals and humans. Females bite to obtain a blood meal. They are inactive at night, preferring to fly in sunlight and avoiding dark and shady areas. Horse-flies are found worldwide with the exception of a few islands and the polar regions.

Adult horse-flies feed on nectar and plant exudates. Males have weak mouth parts and only the females bite in order to obtain protein from blood to produce eggs. The mouthparts of females are formed into a stout stabbing organ with two pairs of sharp cutting blades, and a sponge-like part used to lap up the blood that flows from the wound. The larvae are predaceous and grow in semiaquatic habitats.

Tabanids are known vectors for various blood borne bacterial, viral, protozoan, and worm diseases of mammals such as the equine infectious anaemia virus (EIA). To be included are various species of Trypanosoma which cause diseases in animals and humans. Tabanids are known to transmit anthrax among cattle and sheep, and tularaemia between rabbits and humans.

Anecdotal reports for horse-fly bites leading to fatal anaphylaxis in humans are rare, but individual susceptibility cannot be ruled out. Horse-fly bites are painful and present a weal around the site. Other symptoms may include urticarial, dizziness, weakness, wheezing, and angioedema. If feeling unwell or if the wound becomes infected, it is important to seek medical advice.

Williams, R. (26 July 2013). “Allergic reaction to horsefly bite kills father of four in seconds after anaphylactic shock”The Independent. Retrieved9 September 2015.