Bot flies are large, stout bodied, hairy flies that resemble bumblebees.
But how they reproduce is what makes them interesting: 1) An egg-laden female botfly captures a night-flying female mosquito and glues her eggs on to it. 2) When the mosquito is released and bites a victim, the host's body heat triggers an egg to hatch. 3) It falls off and burrows in. Even more interesting is that sometimes, this happens on humans! [YouTube/NSFSqueamish]
And on humans sometimes, this happens in the most inconvenient [pdf]