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Macrobdella decora, the North American medicinal leech, is a species of freshwater leech found in Canada, the United States, and Mexico. A medium-sized annelid growing up to 8.5 cm (3.3 in) long, it has a spotted greenish-brown back and a reddish underbelly. M. decora is commonly encountered by swimmers and lives in ponds, ditches, and wetlands. The leeches are both blood-sucking parasites and aggressive predators. They have three saw-like "jaws" which they use to penetrate their host's skin, and they can remain attached for up to two hours. Their hosts include fish, turtles, wading birds, and mammals, including humans. The leeches are also voracious predators who eat other invertebrates, amphibian eggs and larvae, and sometimes even members of their own species. M. decora was historically used for leeching by European colonists in North America, who found the native leeches "equally efficacious" as those from Europe. (Full article...)