Wash your damn hands before touching that

Oh boy. Ohhhhh boy. Okay, Bot flies. There are dozens of varieties of Bot Fly, they're each highly adapted to target a specific animal, they have delightfully descriptive names like Horse Stomach Bot Fly, Sheep Nose Bot Fly and, hey, guess what. One of them is called Human Bot Fly.

They each have a different and elaborate reproductive cycle, all of which end with a fat, half-inch maggot embedded in living flesh. Feeding.