Medicinal Leech (Hirudo medicinalis)


Class: Hirudinoidea 
Order: Arhynchobdellae 
Family:    Hirudinidae 
Size:    Length: Up to 5 inches (12.7 cm)
Weight: Unknown
Diet: Blood
Distribution: Europe
Young:  Approximately 12 eggs per season
Animal Predators:  Unknown
IUCN Status: Lower Risk, Near Threatened
Terms: None
Lifespan: Unknown



·         The medicinal leech is the rarest of the over 650 species of leeches.

·         Medicinal leeches live only in fresh water, although some other species can be found in the sea.

·         These animals belong to the same family as worms.

·         It can take a leech several months to digest one meal.



Medicinal leeches are olive green, with four to six reddish brown stripes. They have suckers at both ends, and attach themselves to the skin of a mammal, using their teeth to bite through the skin. The victim is left with a small Y-shaped wound. These leeches have five pairs of eyes at their front end, and teeth at the back end.



Medicinal leeches live both on land (albeit damp areas), where they move in a similar fashion to inchworms, and in water, where they swim. 

Feeding Habits

Medicinal leeches used to feed on cattle and horses that would come by a water source to drink, but with the decreased use of horses, as well as the installation of watering systems on ranches and farms, not as many mammals happen by where leeches live. Luckily, a leech does not need to feed often, because it can suck up to five times its own weight in blood at one time, growing up to 11 times its body size, and can live on that amount of food for up to a year. While the leech is drawing blood, it injects an anaesthetic, enabling it to go unnoticed. It feeds for about 20 to 30 minutes and normally eats twice per year. 



Although all leeches have both male and female organs, they cannot reproduce on their own. In spring, a leech joins up with another leech on land and as a result, both leeches become pregnant. They lay their eggs in a mucous sac in damp soil, close to the water’s edge. When the eggs hatch two weeks later, they are fully formed miniature versions of adult leeches. The young leeches feed on the blood of frogs, because their jaws are not yet strong enough to penetrate the skin of mammals. 


When resting, medicinal leeches lie on the shore, partly out of the water, hidden under large objects. When in water, they can sense shadows from up above, indicating that there may be a mammal approaching.  



Leeches have been used for bloodletting as early as 130 BC, but they became extremely popular from 1825 to the 1840s. They were used for mental illness, headaches, gout, whooping cough, skin diseases and more. By 1850, however, doctors and scientists realized that the practice was weakening and even killing patients, rather than strengthening them by getting “bad blood” out, and the practice fell out of favour. They are still used in medicine today, but for different purposes, such as in reattachment and plastic surgery, to prevent blood clots. Leech saliva released into the blood works as an anaesthetic and lessens the risk of infection.



Medicinal leeches were found in western and southern Europe, but became endangered and even extinct in some parts of their range due to their popularity in medicine during the 19th century. They have been introduced to North America in the wild, and are the focus of conservation efforts in Europe.