Midges are a nightmare but they are not the worst nightmare.
Clegs are the peregrine falcons of the insect realm. They have evolved to be precision attack machines, hungry for blood. They are large insects and the biggest is the heaviest fly in Europe. They are the fastest flying insects and a male glen has been clocked at 90 miles and hour in pursuit of a female. Their eyes are large, taking up most of the front of their heads and their sight is excellent. In the air they perform manoeuvres like a fighter jet. Like all flies they have one pair of wings and what would have been the second pair are modified into organs called halteres which are like drumsticks. They vibrate up and down at enormous frequency and act as gyroscopes to provide flies with unrivalled manoeuvrability.
In Scotland these notorious insects are called Clegs, in England they are known as Horse flies. They have a voracious appetite for blood but, as with midges, it is only the female that bites as it seeks protein for its egg production. Eggs may be laid in batches of 1000 on a stone near water. The larvae live damp soil. The female of the smaller species approach silently and with stealth, often from behind. They are dark shapes glanced out of the corner of your eye as they approach menacingly in hot weather. They don't fly in cold conditions or in the dark. If you are lucky you may perceive one land on your arm or leg before it is to late and then if you have fast reactions you may be able to swat it before it sinks its mandibles into your tender flesh. If you are unaware of the danger, inattentive, or have slow reactions, the cleg may have time to do its worst. It's worst is to slash you with its razor-sharp blade like mouthparts. They are shaped like sabres with serrated edges. A pool of blood oozes out of the wound and the cleg adds an anticoagulant to prevent clotting as it soaks up the nutritious liquid with a sponge. It is little consolation to know that your blood contributes to the production of that batch of 1000 eggs and hence to the next generation of clegs.
The largest of the clegs, which attack horses and cattle are not silent but fly with a buzz reminiscent of a Messerschmitt.
Clegs are found almost everywhere on earth - they are not found in Antarctica, Greenland, Hawaii and Iceland. If you are seeking a cleg-free holiday in the sun Hawaii may be your best option. There is a theory that the black and white stripes of a zebra, as well as serving as camouflage, also confuse clegs and make the zebras less susceptible to bites. In tropic places clegs can be vectors of both human and animal diseases, including anthrax. In Scotland, fortunately they do not carry human diseases.
Clegs get a mention in literature - Aeschylus describes them as driving people mad through their unrelenting pursuit. Shakespeare refers to them as gadflies in Anthony and Cleopatra and in King Lear. In Greek mythology there is the tale of the God Zeus angering his wife Hera by having an affair with Io, a beautiful maiden. Zeus turned Io into a white heifer in order to conceal her but the plan went pear-shaped and the enraged Hera sent a gadfly (cleg) to bite Io continuously and drive her to distraction. She headed east and in her flight bumped into Prometheus (you know, the Titan that gave fire to mankind). He of course, was having his liver continuously eaten by a vulture as punishment for spilling the beans about the secret of fire to mankind but nevertheless had the presence of mind to tell Io that she would later be mother to the greatest of all Heros, namely Hercules. Io escaped across the Bosporous which, appropriately, means Ox-passage.
Well, it is see clear that the cleg is a remarkable insect which gets around in time, space and mythology.
It belongs to the Dipteran family, Tabanidae ; the word Gad means a spike (need one say more) and the word Cleg appears to come from the Norse. So that's their etymology as well as their entomology.