Why do horseflies fly around water?
Unlike mosquitoes, horse flies do not breed in water, they lay
there eggs in animal feces or carcasses as well as moist deadwood.
Horse flies live in the bush and are attracted to movement. When a
horse fly senses (sees) you are around it stalks you like your its
prey. If you just walked through the bush to get to your boat dock,
they will follow you there. If you are out in your boat they will
have followed you from the bush to the boat. Horse flies are
relentless creatures and the only real way to get rid of them when
out on the water is to kill them. Once your out there and have
killed all the horse flies you will notice that there will be none
around. Of course if you go too close to shore, you may be stalked
by other horse fly predators.
The same theory applies to deer flies as well.