March flies: in the Northern Hemisphere they show up in spring so they get this name. Deer flies and horse flies: these names come from some of their favorite targets. All belong to the dipteran family Tabanidae. Deer flies belong to the genus Chrysops while the horse flies belong to the genus Tabanus. They are big, slow, rather obtuse biting flies who cannot take ‘no’ for an answer. They are one of the few animals that I regularly kill because they simply will not give up when determined to get a blood meal. The other day I was out riding my horse and I ended up killing thirty tabanids. They are much slower than houseflies and once they start drilling into mammalian flesh, they are pretty single-minded and easy to swat. If I just tried to chase them away, they would have been back in seconds.
Horseflies are indeed flies, belonging to the great insect Order Diptera because they have only two functional wings, with the second pair being modified into halteres. Their heads are large, with large eyes and short antennae. The body is fat and they are usually slow fliers. They are rather primitive as flies go and seem to be adapted for biting hoofed animals that do not have hands to swat them. My poor, long-suffering horses can only flick their tails, twitch their skin and finally run away to escape the attentions of their attendant horseflies.
A mosquito is a highly adapted blood sucker. It’s proboscis is needle-like and it is so skilled at inserting its mouthparts that its victims are often oblivious to the attack. Not so the tabanids. They are about as subtle as the proverbial kick in the back side. They use the blades of their mouthparts to saw a big gaping hole in the flesh, which hurts far too much to be ignored. Like mossies, only female tabanids actually suck blood. Males eat pollen and nectar but the females need a good protein source in order to produce eggs and mammalian blood is a great source of easily digestible protein. Males can be distinguished from females by their eyes as well as their feeding habits: males have contiguous eyes while the females’ eyes are separated in the middle.
Being flies, tabanids have larval stages. They breed and lay their eggs in swamps, river mud and damp soil amongst rotting vegetation or even on beach sand. The Tabanus larvae are predators on other insects while Chrysops larvae feed on organic matter in the soil. Eventually after several moults and possibly after as much as several years, they pupate and become adults. Most are big, brown and hairy with black or greenish, buggy eyes, but some are banded black and white and one species that I see on my property is black with red eyes. None of them could be described as pretty though, at least not by me.
Because they suck the blood of mammalian hosts, tabanids have been implicated in the spread of trypanosome infections in stock in tropical Africa and a worm infection known as loaiasis in man, also in Africa. Other diseases that they are implicated in spreading include anthrax and tularemia and they are a vector for the filarial worm, also in Africa. In areas with high tabanid populations, cattle can lose condition and milk production suffer because of tabanid bites.
Mostly though, tabanids are just annoying, not dangerous. I have a good use for the ones that I kill. I feed them to my bearded dragon lizard, who is happy to gobble them up for me. Luckily tabanids appear in spring and hang around all summer but the adults die off in the winter so they are very much a seasonal annoyance.
References: CSIRO 1979. The Insects of Australia. Melbourne University Press. http://encyclopedia.farlex.com/family+Tabanidae http://creatures.ifas.ufl.edu/livestock/deer_fly.htm
