Freshwater leech's head sucker. Coloured scanning electron micrograph (SEM) of the head sucker of a freshwater leech (Hirudo sp.). This parasite has two suckers. Its rear sucker is used to attach itself to the victim while its head sucker contains a mouth and teeth, which are used to feed on the blood. Freshwater leeches are found in lakes and marshes, as well as slow-flowing streams. They feed on the blood of fish, amphibians and mammals. Magnification: x100 when printed 10 centimetres wide.