Leeches feed on blood. Having attached itself to the host animal, it pierces the skin and injects an anaesthetic to hide the pain of its bite so that the host does not find the leech and remove it, and an anticoagulant chemical, which prevents the host's blood from clotting whilst the leech feeds. The length of time a leech may feed seems to vary. One surveyor, as an experiment, allowed a leech to feed on him and it fed for 83 minutes. Another, presumably less-hungry individual, fed for just 25 minutes. During a meal, it may extract 15 millilitres of blood, which can increase the size of the leech by anything up to eleven times its normal body dimensions. A leech's meal can sustain it for over six months, but it may also have to wait many months between feeds. During this time, they can digest their own body tissue to avoid starvation. Leeches find their host animals by detecting disturbance in the water, and they can prey on small creatures as well as large. A frog or a newt, for example, can die from excessive blood-loss following an attack by a leech. Leeches may also behave as predators on some species of fish such as sticklebacks, as well as on great-crested newts and marsh frogs. Leeches are often found in the nests of birds such as moorhens, and seem to use them as shelter as well as finding a food source. Dismantling old nests can be a method of surveying for leeches. The eggs are laid in a spongy cocoon on damp ground and, at Dungeness in Kent, they are associated with the roots of willowherb. On nearby Walland Marsh, the eggs have been found in damp turf on close-grazed sheep pasture. Humans are susceptible to parasitism by leeches but, apart from feelings of disgust, most suffer no ill effects. However, medicinal leeches have been used for removing 'bad blood' from human patients for hundreds of years. Although this practice fell into abeyance by the beginning of the 20th century, leeches are once again being used to restore blood circulation following tissue grafts. Leech saliva may also prove helpful in the future, too, as it apparently contains antibiotics as well as anticoagulants that may prove useful in surgery.

This animal has a slightly flattened cylindrical body, divided into 33 or 34 segments. The upperside is dark brown or black with six long reddish stripes, whilst the underside is speckled. There is a disc-shaped sucker at the head end. The leech is famous for sucking blood and the 'mouth' of the animal is situated within the sucker, complete with teeth. The leech also has five pairs of eyes.

The medicinal leech has been recorded throughout Europe as far east as the Ural mountain range. It has a patchy distribution.

The range extends through parts of western and southern Europe to the Ural mountains and the countries bordering the northeastern Mediterranean (Sawyer, 1986).

Biogeographic Regions: palearctic (Native )

The medicinal leech has been recorded in 24 countries throughout Europe as far as the Ural mountain range. It is scarce in France and Belgium, and is thought to occur in more than 20 scattered populations in the UK. These extend from Kent to Argyll and Islay in Scotland, and from Norfolk to Anglesey.

The medicinal leech has a cylindrical, dorsoventrally flattened body divided into thirty-three or thirty-four segments. The dorsal side is dark brown to black, bearing six longitudinal, reddish or brown stripes, and the ventral surface is speckled. All members bear a posterior and anterior disk-shaped sucker. The anterior sucker surrounds the oral opening where the teeth for incison are located. In addition, the medicinal leech has five pairs of eyes located on its front end. H. medicinalis has several pairs of testes and one pair of ovaries as well as a thickening of the body ring, known as a clitellum, which is visible during the breeding season (Grzimek, 1974).

Habitat and Ecology

Systems

• Terrestrial
• Freshwater

The medicinal leech is amphibious, needing both land and water, and resides exclusively in fresh water. A typical habitat for H. medicinalis would be a small pond with a muddy bottom edged with reeds and in which frogs are at least seasonally abundant (Sawyer, 1986).

Aquatic Biomes: lakes and ponds

The leech is an amphibious freshwater animal, and usually found in small pools with muddy bottoms and fringed with reeds. These pools are also shared with frogs, toads or newts for at least some of the year. Leeches prefer water that is eutrophic, meaning it is high in nutrients. Where amphibians are not present in leech infested ponds, it is believed that grazing stock provide the food source. On Romney Marsh in Kent, there are extensive populations of the medicinal leech living in the shallow parts of deep gravel pits, and in ditches that run through the grazing marshes. In Cumbria, leeches have been found in conditions that differ markedly from those in Kent. Here, it is thought that being shallower, the water warms up quickly to about 20°C, a temperature that must be attained for at least part of the year in order for leeches to survive in a pond.

Hirudo medicinalis is parasitic and the adults feed on the blood of mammals. It attaches to the host by means of its two suckers and bites through the skin of its victim. Simultaneously, the leech injects an anaesthetic so that its presence is not detected, and an anticoagulant in order for the incision to remain open during the meal. It has three jaws, which work back and forth during the feeding process, which ususally lasts about 20 to 40 minutes and leaves a tripartite star-shaped scar on the host. After a full meal of 10ml to 15 ml of blood, the medicinal leech may increase 8 to 11 times its initial body size. Leeches only feed about once every six months, this is about how long the blood meal takes to be fully digested. Certain bacteria keep the blood from decaying during the long digestion period. H. medicinalis may even go longer than six months without food by digesting its own tissues.

Young leeches feed on frogs instead of mammals because their jaws are not yet strong enough to cut through mammalian skin (Grzimek, 1974; Sawyer, 1986).

H. medicinalis breeds once during an annual season that spans June through August. It also remains fertile over a period of years,unlike most other leech species. The act of copulation takes place on land, where one leech attaches ventrally to one another by means of a mucus secretion. All leeches are hermaphroditic and fertilization is internal. Sperm is injected into the vagina by an extendable copulatory organ. A cocoon is formed around the clitellum and slips off the anterior section of the leech. The whole egg sac is laid in damp soil usually just above the shoreline. After about 14 days, the eggs hatch as fully formed miniature adults (Grzimek, 1974; Sawyer 1986).

The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There are 15 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
 

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 15
Species: 15
Species With Barcodes: 1

The medicinal leech is rare throughout its range in Europe and extinct in much of its former range. This is due primarily to the overharvesting of leeches in the past century for medicinal use. Other factors contributing to the leech's reduced status is the alteration of its usual habitat and possibly a decrease in the frog population. Frogs are essential for leech development as its young cannot yet feed off mammals for its first two meals (Sawyer, 1986).

US Federal List: no special status

CITES: appendix ii

IUCN Red List of Threatened Species: lower risk - near threatened

Classified as Vulnerable in the UK, listed under Appendix III of the Bern Convention, Appendix II of the Convention on International Trade in Endangered Species (CITES), Annex V of the Habitats Directive, and protected in the UK under Schedule 5 of the Wildlife and Countryside Act, as amended.

Population

Population Trend

Major Threats

Curiously, the medical use of leeches might explain their wide distribution across the country, as they are thought to have been released into ponds once they had been used for bleeding patients. It is also thought that over-collecting reduced their numbers in some areas. Over-collecting for medical purposes is unlikely to be a threat these days, given the protected nature of this species and the ability to breed leeches commercially at leech farms. Conversely, the pharmaceutical industry has funded much of the recent work under the UK Species Action Plan for this leech. In Romney Marsh perhaps the most significant issue has been the conversion of grazing marsh to arable cultivation - resulting in lowering of water levels, pollution, and fewer host species. Invasion of scrub around ponds has also been a problem.

Conservation Actions

The medicinal leech is listed in the UK Biodiversity Action Plans (UK BAP), and is included in English Nature's Species Recovery Programme. As a first step in ensuring its survival as a native species, many of the leech's known sites were designated as Sites of Special Scientific Interest (SSSIs), and a survey was commissioned to establish the species' true status. An obvious requirement of any species of animal is a food source, and for the medicinal leech this source is other animals. The diet of leeches on Romney Marsh is not perfectly understood. Birds and frogs do seem to be major prey items, but fish have been attacked, and it is suspected that mammals are an under-recorded food item. There are several reports of them feeding on sheep. Scrub clearance around the shallow ponds on Romney Marsh has resulted in leeches taking up residence, and they have also colonised a large number of gravel pits on Dungeness originally created for bird conservation. At the site in Kent, which has the UK's largest leech population and is within the RSPB reserve at Dungeness, water birds provide the food source. At another site, Moccas Park lake in Herefordshire, grazing animals use the lake as a source of drinking water, which suits the leech very well.

The medicinal leech is parasitic on humans and is a source of unpleasant emotions for leech victims and bystanders alike (Grzinke, 1974).

The medicinal leech, as its name suggests, has historically been used for medicinal purposes, mainly to remove "bad blood" from the diseased. Around 1850 this practice fell into disrepute, but H. medicinalis is again becoming of value in medicinal practices. Today this species is used to relieve pressure and restore circulation in tissue grafts where blood accumulation is likely such as severed fingers and ears. The anticoagulant of leeches is also a fertile ground of research for surgeries in which an incision must be kept open. In addition, leech saliva is found to contain powerful antibiotics and anaesthetics which no doubt will prove useful in future medicinal practice (Sawyer, 1986).

The medicinal leech (Hirudo medicinalis) has been used during medical surgery to minimize blood buildup. Due to anticoagulant properties in its saliva, this leech has been very useful for this purpose. Medicinal leeches have been important in research for neurobiology, developmental genetics, enteric symbioses, or oncology (Siddall et al. 2007). There have been at least 115 bioactive compounds isolated from medicinal leeches, includin anticoagulants, antistasins, and other protease inhibitors (Siddall et al. 2007), however it appears that these bioactive compounds are not limited to just Hirudo medicinalis but are also found in additional species of European medicinal leeches (Siddall et al. 2007). Many bioreactive compounds isolated from medicinal leeches are still being researched for their potential; further research will show whether the antimetastatic properties of Hirustasin (isolated from medicinal leeches) are without anticoagulant effects that hinder their use in cancer patients (Sollner et al. 1994).

Hirudo medicinalis is a parasitic organism and in various circulmstances, it can negatively affect ecosystems and their inhabitants. It feeds on the blood of vertebrates, especially mammals whose blood holds higher energy content compared to amphibians (Merila and Sterner 2002). In addition to mammals, leeches can also parasitize amphibians (e.g., frogs, toads, and newts) and negatively affect their population dynamics by reducing reproductive success furing the breeding season (Merila and Sterner 2002).