My favourite parasite is back in the news. This is an isopod (a crustacean, closely related to woodlice) named Cymothoa exigua, and here’s what it does: it slips into a miserable fish’s oral cavity and clamps itself on the base of the tongue and commences to drain blood. As it grows on the fish’s expense, the tongue will atrophy and waste away completely leaving but a stub. Then it assumes the role of the tongue and starts acting like a normal tongue! It is no doubt hideous to look at, but it just as much amazes me how this sort of adaptation can come about. It apparently does no other harm to the host, but I still definitely don’t want one in my mouth.