Freshwater leech. Coloured scanning electron micrograph (SEM) of a freshwater leech (Hirudo sp.). This parasite has two suckers, one at each end of its body, that it uses to attach itself to the skin of its victim whilst it drinks their blood. The mouth is contained within the head sucker (upper left) while the rear sucker (upper right) is used to hold the leech on the prey's skin. 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: x25 when printed 10 centimetres wide.