Geographical Range Europe
Habitat Ponds, marshes, ditches with shallow water
Scientific Name Hirudo medicinalis
Conservation Status Near threatened

These small worms have been used by doctors since 500 B.C. They have chemicals in their saliva that help blood flow more freely, some of which are even proven antibiotics. Surgeons sometimes use leeches today to aid healing after microsurgery.

Leeches were frequently used in 18th and 19th century medicine for bloodletting, a process that was believed to cure almost any ailment from gout to headaches -- even the flu. While this practice had been abandoned, the medicinal leech is making a comeback as a valuable assistant to plastic surgeons. They sometimes use the animals to drain off extra blood in delicate tissue, or to help restore blood flow after re-attachment of grafted or severed skin.