The horsefly's mouth works in a scissor-like fashion to slash open the skin, so that the blood seeps out and the fly can lick it up. This makes bites initially much more painful than mosquito bites. When attacking humans, they generally prefer the head and upper body.
Protection: As well as covering up, insect repellent — permethrin and DEET — will deter them.
Worst-case scenario: In Africa, Asia and South America, horseflies are thought to spread Anthrax.
Expert view: Catti Moss says: "When a horsefly bites, you really feel it."
The bite from a larger specimen can be painful, especially considering the light, agile, and airborne nature of the fly. Unlike insects which surreptitiously puncture the skin with needle-like organs, horse flies have mandibles like tiny serrated scimitars, which they use to rip and/or slice flesh apart. This causes the blood to seep out as the horsefly licks it up. They may even carve a chunk completely out of the victim, to be digested at its leisure.
The horsefly's modus operandi is less secretive than that of its mosquito counterparts, although it still aims to escape before pain signals reach their mark's sphere of awareness. Moreover, the pain of a horsefly bite may mean that the victim is more concerned with assessing and repairing the wound, than finding and swatting the interloper.