They are predatory or parasitic segmented worms related to the earthworms, and should not be confused with the land slugs which have no suckers, live entirely on plants, and are snails without shells.
All leeches live in water except a few which are found in moist soil in warm climates.
There are dozens of kinds in the ponds, ditches, lakes and streams of this region, but they are most numerous in quiet shallow water with a soft mud bottom. In early days, the European Medicinal Leech was shipped to America in quantities. A few escaped to natural waters and have become established in New York state. Blood-letting by leeches has been a common medical practice in many parts of the world since ancient times. A leech has a large muscular sucker on the tail end and a smaller one on the head, around the sucking mouth which, in some kinds, is armed with jaws.