His Subject: Highly Evolved and Exquisitely Thirsty

It amazing that bloodsuckers that spread parasites among frogs and fishes are used in medicine as anticoagulants. Carl Zimmer reports on a researcher, Dr. Siddall, from Canada that has an affinity for leeches. Actually, to the point of traveling to far off exotic places to find different kinds of leeches. Turning himself into bait is paying off. Dr. Siddall's research has shown that the ancestors of leeches were probably freshwater worms that fed harmlessly on the surface of fish or crustaceans, as the closest living relatives of leeches do. Not only do these worms have the most leechlike DNA of any animal, but they also grow the same sucker on the base of their tail that leeches use for crawling.