20+ Interesting Facts About Horseflies

1. Horseflies are flying insects belonging to true flies. Their closest living relatives are deer flies, which are smaller than horseflies.
2. There are nearly 4,500 horsefly species. Their size varies according to species, ranging from a housefly to a bumblebee. The dark giant horsefly, nearly 1 inch long, is the largest among horseflies. It is also the heaviest fly in Europe. 
3. The horsefly is one of the fastest-flying insects. Its estimated fastest flying speed is 39 km/h (24 mph). This speed is comparable to that of other fast flyers, such as hawk moths and dear bot-flies. Only dragonflies can achieve a faster speed for short bursts. (Source)
4. Male horseflies feed on the nectar, honeydew, and pollen of plants. Females also drink nectar, but they need blood for reproduction. Only females have mouthparts that can break the skin.
5. Female horseflies usually drink blood from horses, cattle, and other large mammals, including humans. They select dark-colored moving animals through the CO2 they exhale.
6. Horseflies attack darker animals (black or brown) under sunlight. It is because their wing muscles and nervous system work efficiently in high temperatures and on warmer bodies. Therefore, they usually avoid shady areas and light-colored (white or beige) animals. (Source)
7. Horseflies have large, bright, and colorful eyes. Females have completely separate eyes, while eyes in males join dorsally.

   

   Colorful horsefly eyes are sensitive to polarized light

   
   
8. Horsefly eyes are sensitive to polarized light. These insects use the polarized deflection from an animal skin to detect their prey. Therefore, they prefer shiny objects of specific colors. (Source)
9. Horseflies have strong tarsal claws and hooked hairs. They use them to grasp the animal fur when drinking blood.
10. Studies have proved that zebra stripes confuse horseflies and considerably reduce their bites. The number of horseflies’ stings also declines on horses wearing sheets of similar pattern and color. (Source)
11. Horseflies are common in most parts of the globe except Polar Regions and some islands like Hawaii, Iceland, and Greenland. These insects usually avoid deep shades, true deserts, mountaintops, and urban centers with well-managed water systems. 
12. Horseflies are usually present in woody areas around streams and marshes. Females lay up to 1,000 eggs in a cluster and choose moist areas on the grass for egg laying. They prefer 
13. Large populations of horseflies are dangerous for domestic mammals. These flies can transfer infectious diseases like tularemia and anthrax to victims. Additionally, they can reduce milk production in cows and affects animal growth by drinking three ounces or more blood per day.
14. Male horseflies sometimes use a flying technique similar to the Immelmann turn (a vertical U-turn manoeuvre) by jet fighters.
15. It is hard to control horseflies through insecticides due to their flying speed and other features. The more effective measures against horseflies are: keeping animals under shade, putting on zebra-pattern sheets, and using full-body fly repellent.
16. Horsefly bite is more painful than mosquitoes because they lack the mild anesthetic release by mosquitoes. Their saliva contains an anticoagulant that prevents blood clotting and ensures the free flow of blood from the prey.
17. Female horseflies may bite humans, resulting in a painful wound. The risk increases in summer when horseflies need blood and humans roam outside in less clothes. However, these painful bites are less harmful than those of mosquitoes.
18. Horseflies have several natural predators. These include birds, frogs, spiders, wasps, nematodes, and dragonflies.
19. Most flies fly silently. However, horseflies are noisy and produce a loud, buzzing sound during their flight.
20. Both male and female horseflies play a vital role in pollinating some flowers. An example is the pollination of Disa Draconis, an orchid in South Africa, by horseflies. (Source)
21. Horsefly larvae can exit the egg through their spine and fall on the moist ground. Before reaching adulthood, they feed on organic matter, insects, and small crustaceans by using their venom.