Some swamps and ponds contain leeches, worms that can cling to fishes, animals and ever to persons. Leeches may grow from ½-inch to 4 or more inches long.
Like many worms, they have soft, flat bodies divided into segments. On the leech’s head is a sucker like mouth equipped with three saw-shaped teeth. A second sucker is located at the hind end of the leech.
The leech attaches itself to the host by means of its suckers. Then, with the mouth sucker, it sucks up the blood through three little holes which it makes in the skin with its sharp teeth.
In a single meal a leech may eat three times its own weight in blood. One meal may fast several months.
Not all leeches suck blood. Some feed instead on worms and other small animals that live in the water. During medieval times bloodsucking leeches were used by physicians to draw blood from patients in attempts to cure them. – Dick Rogers