Leeches are nasty, horrible creatures. I think it would be pretty difficult to find someone who really likes leeches, unless they’re a leechologist. Still, leeches do have a place in this blog, as I try and cover as wide a range of animals as possible. So today we will discuss the most famous of leeches, the medicinal leech.

There are a number of species of leech that have been used in medicine, but the most common one is the European medicinal leech. They are found mostly in Europe, but also as far east as Kazakhstan and Uzbekistan. Leeches prefer to live in gross muddy ponds, which seems fitting for such unloved creatures.

A nice close up of a leech. Image by Heaporgand, CC BY-SA 4.0, via Wikimedia Commons

Leeches are types of worms, and the medicinal leech looks pretty worm-like. They can grow to be fairly long, reaching 20 cm. They have two suckers, one on each end of their bodies. The one on front end of the leech has teeth on it, and is used for sucking blood, while the sucker on the other end of the body is used as leverage. Medicinal leeches are generally dark brown or black, with six red or brown stripes running down the lengths of their bodies.

Medicinal leeches have the lovely dietary habit of subsisting solely on blood. They latch onto their hosts using their suckers, and their saliva contains a nice cocktail of substances that ease the feeding process. An anesthetic prevents the hosts from feeling pain, so the leeches remain undetected, while a bunch of anticoagulants keep blood flowing nicely.

After a 20 to 40 minute meal, leeches ingest up to 10 to 15 ml of blood, and can be 11 times their original size. These amazing animals only have to eat every six months or so, as their digestive system works quite slowly. You might think the blood would go bad in such a long time, but leeches have solved this problem by having bacteria in their stomachs that keep the blood nice and fresh.

A leech attached to human skin. So pleasant. Image by GlebK, CC BY-SA 3.0, via Wikimedia Commons

Leeches mate from June to August, when they move to land to meet other sexy leeches. They hermaphroditic, and attach to one another through a mucus secretion during copulation. Sounds romantic, doesn’t it ? The leeches lay their eggs on land, near their home pond and just above the water line. The young leeches hatch in two weeks, and look like miniature adults. Their jaws are not as strong as those of a fully formed leech, however, so they feed on frogs until their jaws are strong enough to pierce mammal skin.

Though leeches are not endangered, they are near threatened, thanks for over-harvesting in the 19th century. As well, drainage of land and decline in frog populations have contributed to the medicinal leech’s decline. They are still used in medicine today, though I’m not sure I’d want any doctor putting a leech on me. They’re just too creepy.

Cover image by Holger Krisp, CC BY 3.0, via Wikimedia Commons