Leech (Hirudinea) photographed on the Grand Manan Island off the coast of New Brunswick. These leeches were quite common in the fresh water bogs on the island. Leeches are parasites which feed on blood. They attach themselves to the skin using suckers and create a wound with their three sharp jaw plates. Their saliva contains hirudin, a chemical which prevents the blood from clotting. A leech may drink between 10 and 15 milliliters of blood in one meal, which will feed it for months.