Leeches are worms that live off of blood or hunt small aquatic animals. They have a tough, moveable body and two suction pads, one in front and one in back. Small teeth are located in the front suction pad, which are used to make wounds. There are around 30 known species in the Netherlands, of which only one rare species attaches to people. A troublesome parasite for fish is the common fish leech and for water fowl the duck leech.