The horse leech has a body length of up to 15 cm. The spine in an adult species is brownish-black, sometimes with dark speckles. The young have a lighter spine, with a visible symmetrical pattern. The belly is greenish-grey to grey. Characteristic yellow bands along the sides can be absent in many species. The attachment sucker at the posterior end is small, less than one-half of the body width.
The horse leech mostly occurs is shallow ponds and puddles, or in moist mood of drying puddles. It can also be found at the edges of lakes and rivers. The horse leech is common throughout Europe, Asia, and the Far East.
The horse leech swims by bending its body in a wave-like pattern. Horse leeches are not dangerous to humans or large animals, they are unable to bite through their thick skin. They breed in summer, at three years of age, by laying egg cocoons in moist sand at the edges ponds or puddles. The hatching of the leech's eggs takes around 30 days. The newborn leeches leave the eggs completely independent. Horse leeches are strong and voracious predators feeding on worms (including other leaches), molluscs, water insect larvae, tadpoles and other pray that they are able to attack.