So this big old bumblebee of a fly snatches a mosquito or house fly out of the air by grabbing onto it's wings then lays it's eggs on the captive's behind (harmlessly.) When the housefly or mosquito land on an animal (or human) the body heat causes the eggs to hatch and land on the host's skin. The larvae burrows into the skin and causes what appears to be an abscess. Until it starts to wiggle.
Then you have this:
Whatever you do, don't read this:
The damn things catch an intermediate host because they are too large to approach unnoticed, and their wings make noise. So they get a smaller, quieter insect to carry the eggs for them.
Now I am so totally paranoid of mosquitoes and houseflies. WASN'T WEST NILE ENOUGH?
Once the larvae are mature they drop out of the host and burrow into the ground where they transform into an adult and start the whole thing over.