Besides
this thing this little critter's what comes to mind when I hear the word parasite...
The Bot Fly
Pretty nasty thing this. I know it comes from tropical areas (I forget exactly where though), but the coolest thing about it is that the female bites cattle and horses and lays her eggs under their skin which in turn, naturally, live as parasites under the skin staying warm from the host mammal's body heat until they hatch. There's a species of bot fly which does this with humans too, like so;
Pretty neat huh