All leeches are very extensile and can contract the body to a plump, pear-shaped form, or extend it to a long and worm-like shape.
Small leeches taken into the mouth with drinking-water may give rise to serious symptoms by attaching themselves to the fauces and neighbouring parts and thence sucking blood.
The rivers and lakes yield enormous quantities of fish, and leeches also are plentiful.
Leeches are usually olive green to brown in colour, darker patches and spots being scattered over a paler ground.
The Oder and some of the tributaries of the Elbe abound in crayfish, and in the stagnant lakes of East Prussia leeches are bred.