The screwworms are really scary. The tongue-biter is amazing.
Six horrifying parasites: "Mark Frauenfelder: Neatorama has a nice article about six sickening parasites.
A female sacculina begins life as a tiny free-floating slug in the sea, drifting around until she encounters a crab. When that fateful day arrives, she finds a chink in the crab's armor (usually an elbow or leg joint) and thrusts a kind of hollow dagger into its body. After that, she (how to put this?) 'injects' herself into the crab, sluicing through the dagger and leaving behind a husk. Once inside, the jellylike sacculina starts to take over. She grows 'roots' that extend to every part of the crab's body -- wrapping around its eyestalks and deep into its legs and arms. The female feeds and grows until eventually she pops out of the top of the crab, and from this knobby protrusion, she will steer the Good Ship Unlucky Crab for the rest of their co-mingled life. Link(Thanks, Frank!)
(Via Boing Boing.)