Nature: Leeches

This fact sheet on the biology of leeches, which "are commonly found in lakes and ponds and many of [which] provide food for vertebrates such as fish, ducks, turtles and some other birds," also discusses the history and current uses of leeches for medicinal purposes. <http://dnr.metrokc.gov/
wlr/waterres/Bugs/Leeches.htm>