At a glance
Essentials
- Size
- Up to 20 cm in length in mature adults. The range may vary with age, sex and population.
- Distribution
- Much of Europe, extending towards Asia as far as Kazakhstan and Uzbekistan.
- Habitat
- Freshwater, especially muddy ponds and ditches with abundant vegetation in temperate climates.
- Activity
- Hermaphrodite; reproduces by sexual mating, depositing eggs in humid and shaded places near the water.
- Diet
- Feeds on the blood of mammals, reptiles, and amphibians.
- Conservation
- Near threatened (IUCN); populations reduced by historical overexploitation and habitat degradation.
Observation guide
What to look for
- 01
Adults up to 20 cm in length, with green, brown, or green-brown coloration, darker on the dorsal side and lighter on the ventral side.
- 02
Three toothed jaws (mandibles) that leave a bite mark in the shape of an inverted Y within a circle.
- 03
Body formed by 34 metameres, without setae or parapodia, and with a visible clitellum.
Lighting, age and viewing angle can hide features. If identification affects consumption, handling or conservation, consult specialist sources.
Ecology
Description and characteristics
The medicinal leech (Hirudo medicinalis) is a species of annelid in the family Hirudinidae, classified within the order Arhynchobdellida. Its body, which can reach up to 20 cm in length in mature adults, exhibits a coloration that varies between green, brown, and green-brown, with a darker tone on the dorsal side and a lighter one on the ventral side. Unlike other annelids, it lacks setae and parapodia, and its body is formed by 34 metameres without internal partition walls. It possesses a clitellum that secretes an incubation capsule for the offspring. On the underside, it presents a buccal sucker, a mouth armed with three toothed jaws (mandibles) used to cut the skin, a posterior sucker, and an anus. These jaws, which resemble saws with approximately 100 sharp edges, allow it to incise the host's skin, leaving a characteristic mark in the shape of an inverted Y within a circle. During feeding, the leech sucks blood while injecting anticoagulants, such as hirudin, which prevent coagulation and maintain blood flow in the wound and in its own digestive system. The genome of this species contains multiple known anticoagulation factors, which underscores its biological and medical importance.