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European Medicinal Leech: Features, Biology, and Medical Use

Linda Crampton is a writer and experienced science teacher with an honors degree in biology. She enjoys writing about science and nature.

Hirudo medicinalis in the sucking position

Hirudo medicinalis in the sucking position

An Intriguing and Useful Organism

The European medicinal leech (Hirudo medicinalis) is an intriguing organism. It’s related to earthworms and has a segmented body. Leeches are classified as either parasites or predators. The parasites include the medicinal leech. They feed on liquid blood, which they obtain from their host with the aid of a chemical in their saliva called hirudin. The substance acts as an anticoagulant.

The blood-sucking habit of the medicinal leech is used to help specific health problems in humans, as its name suggests. Precautions are needed when the animal is used for medicinal purposes. These precautions are described in the “Warning” section below. Scientists have recently sequenced the genome of the leech, which might lead to some interesting and hopefully useful discoveries.

Several species are referred to as "medicinal leeches". In this article, I use the term to refer to the European medicinal leech, or Hirudo medicinalis. The species is used in medicine in Europe and in other parts of world. The International Union for Conservation of Nature (IUCN) classifies the wild population of the species as Near Threatened.

External Features of Leeches

Leeches belong to the phylum Annelida, like earthworms. They are usually classified in the class Clitellata within this phylum and in the subclass Hirudinea within the class Clitellata. Some sources refer to the Hirudinea as a class instead of a subclass. Leeches in general (including the medicinal leech) have certain features in common, including the ones described below.


The body of a leech is long and worm-like or short and wide, depending on the species. The members of the phylum Annelida are segmented on the outside of their body and on the inside.

According to the latest analysis, leeches have 34 internal segments. The animals have a larger number of external segments than internal ones. In some leeches, the external segments are obvious, while in others they are barely visible.

The Clitellum

One reason why leeches are classified in the class Clitellata is because part of their body is surrounded by a thickened area called a clitellum. Unlike the case in earthworms, a leech's clitellum is noticeable only during the reproduction period.

The clitellum produces a ring of secreted material that surrounds the body. The ring picks up eggs and sperm from openings in the animal as it moves forward towards the leech's head. It eventually slides off the head and forms a cocoon. The process is shown in the video below. The youngsters develop inside the cocoon.

Habitat, Suckers, and Movement

Many leeches live in fresh water, but some species live in the ocean or on land. Aquatic leeches can swim through the water by moving their body in an undulating style. On land, the animals often inhabit moist areas in forests. The land animals don't seem to enter water deliberately, but many can survive a short period of immersion.

According to the Australian Museum, some terrestrial species burrow into the soil when the environment is dry. Their body dries out and becomes rigid. If the soil is moistened, the animals quickly revive.

A leech has a small sucker surrounding its mouth at its anterior (front) end and a larger sucker at the posterior (rear) end. The suckers are visible only in certain situations. The anterior sucker attaches the leech to its victim. The posterior sucker also attaches the animal to the victim and in addition provides leverage during movement over a solid surface. Leeches often use a looping or "inch worm" style of movement when they are approaching a suitable host. The animals have muscular bodies.

A human neuron (or nerve cell) showing the dendrites, cell body, and axon; the axon may be much longer than shown

A human neuron (or nerve cell) showing the dendrites, cell body, and axon; the axon may be much longer than shown

Nervous System and Senses

Neurons or Nerve Cells

As in us, the nervous system of a leech is based on neurons, or nerve cells. A neuron contains a cell body containing the nucleus. The cell body has one or more extensions. A dendrite is an extension that conducts a nerve impulse towards the cell body. An axon is an extension that conducts a nerve impulse away from the cell body and to the next neuron. Multiple types of neurons exist. They are similar but not identical. The illustration above shows a common type found in humans that has multiple dendrites.

Brain and Ganglia

A leech is sometimes said to have a brain in its head, but the structure has a different composition from the brain of more advanced animals. The head region of a leech contains two connected ganglia. A ganglion contains the cell bodies of multiple neurons.

Axons from the leech's head extend along the animal's body as a nerve and meet another ganglion, which is known as a segmental ganglion. This in turn extends its axons along the body as a nerve until another segmental ganglion is reached. The process repeats along the length of the animal. Closely aligned ganglia are located at the end of a leech, which are known as the tail ganglia or the posterior brain. Branches leave the main nerve cord and go to various parts of the body.

Sense Organs

The head of a leech has small eyespots or ocelli that can detect light but can't form an image. One to four pairs of eyespots are present, depending on the species. Sense organs around its head enable the animal to detect the presence of certain chemicals in its environment. The animal is also able to detect vibrations and environmental temperature via sense organs on its surface,

Though some websites say that leeches have 32 brains, the "brains" are really ganglia and are much simpler than the brains of many more advanced animals.

The Digestive Tract and Digestion

The digestive tract of a leech travels from the mouth to the anus. It consists of a pharynx, an esophagus, a crop, a stomach, an intestine, and a rectum.

The crop is an elongated structure with ten chambers, which are positioned one after the other along the digestive tract. Each chamber has a sac on either side called a cecum. The crop and its ceca act as a storage site for ingested blood. The blood may be stored there for months. If a blood-sucking leech gets a good meal, it may not have to eat again for a long time.

The crop leads to a small stomach, which digests the blood. The digested material is absorbed by the lining of the intestine. The undigested remains of the food are sent to the rectum and then out of the body via the anus, which is located on the dorsal (upper) surface of the animal.

Some medicinal leeches (Hirudo medicinalis) are attractive animals.

Some medicinal leeches (Hirudo medicinalis) are attractive animals.

Circulation, Respiration, and Excretion

A leech has a closed circulatory system. This means that the blood (or the haemocoelomic fluid as it's sometimes called) is always within vessels. A dorsal vessel travels above the digestive tract and a ventral vessel travels below the tract. They are connected by lateral vessels that are contractile and act as hearts. The fluid flows forward in the dorsal vessel and backward in the ventral one. Smaller vessels are connected to the main ones.

In the medicinal leech, gas exchange during respiration occurs through the body surface. Oxygen enters the body and carbon dioxide leaves it. The animal doesn't have lungs or gills.

The leech has pairs of nephridia along its body. A nephridium is an excretory organ that removes wastes from body fluids. The wastes are release into the outer environment through nephridiopores.

Reproduction Facts

Leeches are hermaphrodites, which means that a single animal produces both eggs and sperm. A leech mates with another member of its species in order to exchange sperm instead of undergoing self-fertilization.

The testes are arranged in pairs along the middle section of the body. The number of pairs depends on the species. The sperm from the testes is released into a tubular system that leads to an opening on the ventral or lower surface of the body. A leech has only one pair of ovaries. These are located just in front of the first pair of testes and produce the eggs. Like the sperm, the eggs reach an opening on the ventral surface of the body via a tubular system.

Once they are released, the sperm and eggs are picked up by the moving ring of material produced by the clitellum. The juveniles that develop from the fertilized eggs resemble the adults in appearance except with respect to their size.

Medicinal Leeches

The term "medicinal leech" often refers to Hirudo medicinalis, especially in Europe. Other leech species are sometimes referred to as medicinal leeches, however. The "product" listed and approved for medical use by the FDA (Food and Drug Administration) in the United States is the Hirudo medicinalis species.

The European medicinal leech has a thick and segmented body. The upper surface is mostly greenish brown to dark brown but is decorated with green, yellow, orange, or red stripes or blotches. The undersurface is usually lighter in color and may be green, orange, or yellow. The animal sometimes appears to be entirely dark brown or even black. When examined closely under the right lighting conditions, other colors may appear and the leech may look quite attractive.

Most leeches suck blood to obtain nutrients, but some eat animals or decaying plant material instead of blood.

Life of Hirudo medicinalis

Hirudo medicinalis lives in Europe and parts of Asia. It's reared in medical labs in other parts of the world as well as in its native habitat. In nature, the species is found in freshwater habitats such as ponds, shallow lakes, and marshes. Its diet isn't restricted to mammalian blood. It will feed on the blood from mammals that enter the wetland, but it also feeds on blood from other animals, including frogs, turtles, and fish.

The animal has a tripartite (three-part) jaw, which is said to cut human skin with little pain. The leech drops off its victim's body once it's full. Often, the bite seems to do little harm, especially if the animal that's bitten is large. If the leech transmits an infection or if multiple leaches attack the victim, however, the effects may be serious.

Hirudo medicinalis that has been preserved in alcohol, which causes color loss; photo C shows the anterior sucker

Hirudo medicinalis that has been preserved in alcohol, which causes color loss; photo C shows the anterior sucker

Production of Medicinal Leeches

Medicinal leeches were once a popular medical treatment. They fell out of favor for a while but have now become popular again for specific conditions. They must be applied by a medical practitioner who understands how to deal with the animals and how to help and protect the patient. In addition, they must be produced under suitable conditions.

Medicinal leeches are generally bred in medical laboratories in a specific and often sterile environment. A BBC report referenced below describes a leech farmer in Wales, however. His leeches are used by doctors, so he must rear the animals in suitable conditions. The article says that the leeches are starved for six to nine months so that they are hungry when they are placed on a wound.

Incredibly, the leech uses 15 different proteins known to negatively affect the blood-clotting mechanism in vertebrates, and 17 other proteins that are likely also part of the same anti-clotting process

— Sebastan Kvist, Royal Ontario Museum, via ScienceDaily

Leech Therapy

The saliva of a medicinal leech contains a chemical called hirudin, which acts as an anticoagulant. Hirudin is a protein (or a peptide) made of 75 amino acids joined together. Peptides are shorter chains of amino acids than proteins, but the point where a peptide is said to become a protein varies.

Hirudin is a potent anticoagulant. Leech saliva contains other anticoagulants. According to the press release from the researchers studying the genome of the medicinal leech, the saliva of Hirudo medicinalis and the closely related Hirudo verbana "contains the strongest blood thinners known to medicine". It's often claimed that leech saliva also contains an anesthetic, which prevents a victim from knowing that it's been bitten, but some researchers doubt whether this anesthetic actually exists.

Leech therapy is used in some cases of reconstructive surgery, such as finger reattachment and skin grafts. It's beneficial in circumstances in which blood flow through transplanted tissues is required and in which blot clots would be harmful. The leeches are allowed to suck blood for a limited amount of time. Somewhat sadly after their service to humanity, they are then killed. A leech that has fed on one human's blood mustn't be used to treat someone else due to the possibility of disease transmission. Doctors sometimes administer an antibiotic with a leech treatment in case bacteria already present in the animal hurt the patient.

The Sequenced Genome of Hirudo medicinalis

A group of researchers coordinated by the Royal Ontario Museum in Canada has sequenced the genome of the medicinal leach. The genome is the complete genetic information (or set of genes) in an organism. Genes control many of the characteristics of an organism. A gene is a section of a DNA or deoxyribonucleic acid molecule that codes for a particular protein. Cells make the proteins coded for in their genes, depending on certain factors. The researchers hope that their analysis will enable scientists to better understand the medicinal leech's abilities and potential uses and perhaps help physicians to decide when leech therapy is appropriate.

The research could also be useful in another way. Hirudin is available as an isolated protein. Other proteins in the leech's saliva may also be helpful in dealing with human health. If we know which sections of a leech's DNA code for these chemicals, we may be able to add the relevant genes to bacteria. Bacteria are sometimes able to make the proteins coded for in the DNA that is added to them by scientists. Some species of bacteria are able to reproduce frequently under suitable conditions, which might enable a large population with a beneficial gene to be produced.

The posterior sucker of a medicinal leech that has been preserved in alcohol

The posterior sucker of a medicinal leech that has been preserved in alcohol

Therapy From Nature

Nature has provided us with some useful ways to treat certain health problems, though some methods may need to be modified before they are used. It's interesting that an old treatment like leech therapy is being used again.

Hirudin may not be the only medically useful chemical in medicinal leech saliva. The saliva contains multiple chemicals and appears to be beneficial for additional human health problems. People with certain pre-existing health conditions shouldn't be treated by leeches, however. A doctor's advice is very important for anyone considering leech therapy. Provided this advice is sought, we may find that leeches can be very helpful for us in the present and perhaps even more so in the future.


  • Facts about the Hirudinea from the Natural History Museum in the UK
  • Information about leeches from the Australian Museum
  • Freshwater leech facts from the Mountain Lake Biological Station, University of Virginia
  • European medicinal leech entry from the IUCN Red List
  • The European medicinal leech Hirudo medicinalis: L.: Morphology and occurrence of an endangered species by U. Kutschera and Joy Elliott from the Zoosystematics and Evolution journal
  • Leeches farmed in Wales from the BBC (British Broadcasting Corporation)
  • Medicinal leech product classification from the U.S. Food and Drug Administration
  • Genome of Hirudo medicinalis sequenced from the ScienceDaily news service

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2020 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on July 29, 2020:

Hi, Adrienne. I agree. Leeches are interesting animals. It's great when they can help people.

Adrienne Farricelli on July 29, 2020:

Leeches are interesting and apparently quite beneficial, despite the fact that I think most people would cringe about using them. It's reassuring though that under doctor's orders the risks for infections and excessive blood loss can be minimized.

Linda Crampton (author) from British Columbia, Canada on July 14, 2020:

Thank you, Nithya. Leeches can be very useful.

Nithya Venkat from Dubai on July 13, 2020:

An interesting and informative article about the European Medicinal Leech. The anticoagulant properties can be helpful in treating diseases that affect the blood flow .

Linda Crampton (author) from British Columbia, Canada on July 11, 2020:

Thank you very much, Umesh. I appreciate your comment a great deal.

Umesh Chandra Bhatt from Kharghar, Navi Mumbai, India on July 11, 2020:

Detailed, exhaustive and excellent article. Well presented.

Linda Crampton (author) from British Columbia, Canada on July 10, 2020:

Thank you very much, Nishika. I appreciate your comment.

Nishika Chhabra from India on July 10, 2020:

This is surprising! I never knew that they can be medicinally helpful. Thankyou for always sharing such informative articles Linda :)

Linda Crampton (author) from British Columbia, Canada on July 10, 2020:

Hi, Devika. Leeches can be surprising. I hope scientists learn more about them.

Devika Primić from Dubrovnik, Croatia on July 10, 2020:

Linda this is interesting and informative about leeches. The medicinal value is still available that surprise me.

Linda Crampton (author) from British Columbia, Canada on July 09, 2020:

Hi, Mary. I remember being scared of leeches as a child, too. I didn't like the idea of an animal attaching to my skin and sucking my blood! I think they are fascinating creatures now.

Mary Norton from Ontario, Canada on July 09, 2020:

This article is very enlightening, Linda. But I have to tell you; I was super scared of leeches as a child. It was only much later when I read about its medicinal value.

Linda Crampton (author) from British Columbia, Canada on July 09, 2020:

Hi, Denise. Yes, there are several points to consider with respect to leech therapy. It's an interesting topic to explore, though.

Blessings to you as well.

Denise McGill from Fresno CA on July 09, 2020:

I can see how a powerful anticoagulant could be helpful but the idea still turns my stomach. It makes sense that the animal is killed after one treatment but also a bit cruel. Although I admit I'm not as upset about that as I would be if it were a cute cuddly creature.



Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Thank you, Pamela. I appreciate your comment very much.

Pamela Oglesby from Sunny Florida on July 07, 2020:

This is such an interesting article. I have read about leeches and blood letting in the past but this article gives so much important information and I learned a lot. Thanks for all the details about this leech, Linda!

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

It must have been interesting to see the live event.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

The potential medical benefits of leeches are exciting. I hope scientists soon learn more about the benefits and discover more details about how the chemicals in the saliva work.

Danny from India on July 07, 2020:

Yes you are correct. It too was wondering that since COPD, Asthma and other respiratory ailments concern the lungs majorly.

I have seen this tresatment LIVE in South India wherein they send a small murrel fish down the thraot, it eats up the mucus and go down to the stomach.

You are right when you said it doesnt serve the purpose but the fact is some people are relieved form Asthma symtoms .

Even people are skeptical and they have doubts on this treament :)

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

I understand that Danny, but what I am saying is that asthma is not a disorder of the throat and the digestive tract. The problem is in the lungs. If researchers have discovered that once the fish have been digested, chemicals from them are sent to the lungs via the bloodstream and are then beneficial for asthma, that would be wonderful.

Danny from India on July 07, 2020:

Leeches are very helpful to remove toxins and dead cells and restoring the area. Their saliva secretes special proteins which help to ease pain, and keep the blood flowing.

First attmept i didnt elaborate more Linda. :)

Thanks for your consideration.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Thanks for the comment, Danny.

Danny from India on July 07, 2020:

Regarding asthma treament using fish, its a traditional system of curing respiratory ailments using 3-5 cm murrel fish which goes down the throat clearing it all the way down to the stomach. It is not to the lungs but through the throat passing all the way down.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Thank you, Fran. I think leeches are very interesting animals.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Hi, Peggy. Thanks for the comment. I'm looking forward to future discoveries about the uses of leeches in medicine.

Danny from India on July 07, 2020:

Aplologies wrong use of word, its dead cells not stale. :)

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Hi, Linda. I think the potential uses of leeches in medicine are fascinating. The animals have a bad reputation in some places, but they could be very useful for us.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Thank you for the comment, Danny. It’s interesting to read about traditional medical treatments. Sometimes they are helpful, but I think the situations that you mention need some clarification.

Blood is continually circulating through the body. Old red blood cells and wastes are removed and oxygen and new red blood cells are added. Under normal conditions, blood doesn’t get stale while it’s inside the body. I have read about experimental leech use in certain abnormal conditions that I didn't mention in the article, however. Either the removal of blood or substances in the leech's saliva may have been helpful in these situations. I hope more research is done. The possibilities are exciting.

A live fish wouldn’t stay alive for long after being swallowed, and it would enter the stomach, not the lungs. In addition, mucus in the lungs is only one of the problems in asthma. The lining of the airways becomes inflamed and swells, which reduces the amount of oxygen that reaches the lungs.

fran rooks from Toledo, Ohio on July 07, 2020:

Great informative article. I've read about leeches before and the benefit they can be in medicine. Thanks for the article.

Peggy Woods from Houston, Texas on July 07, 2020:

I have read about the old-time use of leeches in medicine, and the fact of them still being used on occasion. Your article fills in many more details about them that I did not know. Thanks!

Linda Chechar from Arizona on July 07, 2020:

I remember the movie about "The African Queen". Humphrey Bogart got into the river and had leeches on his legs. Ugh!

Leeches were also used for historic medicinal bloodletting in ancient texts.

Danny from India on July 07, 2020:

Leeches are used to suck stale areas and restore them. In India, they insert a small fish through the throat to treat Asthma, and it's very effective. The fish travel through the throat and eats up all the mucus.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Thank you for the visit and the comment, Swati. I think that leech therapy is an interesting topic.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

It's interesting to hear that you've used medicinal leeches, Manatita. I hope the new discoveries are useful.

Swati Khandelwal from Nainital on July 07, 2020:

Wonderful information, I have not heard anything about this before. Leech therapy, sounds interesting.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Thank you very much, Eric. I think the genetics part is interesting, too. The analysis of the leech's genome could be very useful.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

I've never been bitten by a leech (as far as I know). I think they are interesting creatures, but I wouldn't like to get bitten by one in my backyard!

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

I understand the idea that they are both fascinating and gross! Thanks for the comment, Bill.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Hi, Manuela. I agree. It is great when natural therapies help us.

manatita44 from london on July 07, 2020:

Amazing stuff!

I used them many years ago in Hammersmith, London. Don't know about their uses now, but yes, there is probably room for new discoveries. A fascinating creature and yes, some are not so bad-looking after all, Haha.

Eric Dierker from Spring Valley, CA. U.S.A. on July 07, 2020:

Well I did not anticipate such a all encompassing article. This was really good and educational. I will look at the biology parts with my son. A relative of the earthworm eh?

That Genetic stuff is so interesting.

Liza from USA on July 07, 2020:

Oh boy, I heard a lot about the leeches used for medical purposes. It's interesting to know so many facts about the sucking blood creature.

I remember when I was a kid, my siblings and I was playing in the backyard, I got bitten by a leech but, I didn't realize it until I get home, and my mother saw a bloodstain on my pants. Thank goodness I didn't get any effects from it.

Bill Holland from Olympia, WA on July 07, 2020:

It's amazing to me that leeches are still used in medicine. They kind of gross me out, but they are fascinating creatures for sure. Thanks for the information. I hope I never need them. :)

Manuela from Portugal on July 07, 2020:

Wow, I wasn't aware of leech therapy, it is great that we can use natural processes to heal us.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

I appreciate your comment, Maren.

Linda Crampton (author) from British Columbia, Canada on July 07, 2020:

Thank you, Jana. It's interesting that an old remedy is helpful today.

Maren Elizabeth Morgan from Pennsylvania on July 07, 2020:

Excellent information.

Jana Louise Smit from South Africa on July 07, 2020:

A great article, Linda. I didn't know that leeches were still being used in a medicinal way. Thanks for sharing this with us. :)

Linda Crampton (author) from British Columbia, Canada on July 06, 2020:

That sounds like a good use for medicinal leeches. Thanks for the comment and for sharing the information, Flourish.

FlourishAnyway from USA on July 06, 2020:

Very interesting biology on this what’s old is new again medical treatment creature. My sister’s ex-husband has a bad case of hemochromatosis (iron overload, a genetic-linked condition). It can cause liver, heart and other serious ailments if the iron isn’t released which usually can be done via regular blood donations. The ex is a wimp, however, and cannot tolerate needles so they offered up medicinal leeches and he balked at that. He decided to live with the damage of iron overload. I was intrigued when I heard about the leaches though.