Horse flies are not regular flies. They are mutant, blood-sucking monsters, trolling the pasture for victims. And they do not die easily. Smacking them with your hand merely stuns them. You must then grind them underfoot until they are mere pieces of fly. Or stab them in the heart with a silver dagger - whichever is easiest. This means it is rare to find a dead, intact horse fly. But I did! The little demon was on our deck, kicking back with a cool drink, taking a break from the blood fest in the pasture. And my daughter smacked him with a flyswatter. Hard. Twice. And he died. So for demonstration purposes, I killed a regular housefly (yes, I took a life needlessly) and placed it beside the horsefly and took their picture:
See? Now are you scared?