Leaches

LEECHES and earthworms are members of a large group of animals known as an­nelids, or segmented worms. The leech's body is always divided into segments.
Leeches are temporary parasites which feed upon the blood of higher animals. You know that the animal upon which a parasite feeds is called a host. Frogs, turtles, cattle, and sometimes human beings, may be the hosts of leeches.

Blood is not the only food of leeches. They will eat tadpoles, snails, worms, and other small animals living in ponds. Differ­ent kinds of leeches have somewhat differ­ent food habits. Thus, a leech may be a cannibal, a scavenger, a parasite, or a free-living animal, but it is said that he will usually make a meal of blood when he can get it.
Years ago many people believed that let­ting blood from a patient's body would cure his illness. The large medicinal leech which was often used for this purpose can take two or three times its own weight in blood into its body at one feeding. The leech's saliva mixes with the blood of the host and prevents it from clotting while the leech is feeding. After a meal, its body is short and broad, and it will drop off the host of its own accord. A leech digests blood slowly and can live on a single meal for a long time.
Leeches usually have three jaws and make a Y-shaped incision. The Australian land leech has only two jaws and makes a V-shaped incision. Australian leeches can vary in size from about 7 mm long to as much as 200 mm when extended.

A leech does not have gills or lungs for respiration. Many fine blood vessels near the surface of his body take in oxygen and give off carbon dioxide.
You may see leeches swimming through the open water or moving over submerged plants or logs. A sucker is located at each end of the leech's body. The mouth is in the oral or anterior sucker. The posterior suck­er is at the other end of the leech's body. Like his relative, the common earthworm, a leech does not have legs. His suckers are useful not only to attach his body to some object but assist him in locomotion as well. When he moves he may remind you of a measuring worm.


Large leeches are about six inches long. Adults of others are from one to four inches in length, but you may find young ones which are quite small. Leech eggs are usually covered with a cocoon which the parent attaches to stones or other objects. A few leeches bury their egg cocoons in moist earth. Others living in streams on the under surface of stones have the odd habit of attaching their eggs to their own bodies. After the eggs have de­veloped into young leeches, you may see dozens of them clinging to the under side of the parent's body.