The Botfly is actually a pretty large fly. Big enough so that you would notice if it landed on you and it would be unable to drop it's parasitic babies off. So instead of doing this itself it finds a house fly, pins it down and attaches its eggs to the smaller fly's abdomen. So, when the house fly lands on you to drink your sweat the heat from your body warms the botfly eggs and the parasitic grubs squirm out and burrow into your arm. Awesome!!!