Can you imagine one of your friends clinging onto you, sucking your blood and increasing in weight by five times! That's what some leeches do! A leech can cling onto sticks, stones, an animal or even you by means of a suction cup. After attaching to an animal, the leech scrapes open a little hole in the skin of its host and releases a chemical that keeps blood from clotting. This leech's strange feeding habit puts it into a special category called a parasite. Other leeches eat a more "civilized" diet of dead plants and animal matter. The presence of a lot of leeches is a sign of mucky bottoms. The leech does not have gills or lungs. It gets oxygen through its skin. Many fishes find leeches great food, they're an important part of a pond's food web.