Classification & Relationships
Leeches are related to earthworms and lugworms (Oligochaetes), and bristle worms (Polychaetes). But unlike other worms they have a sucker at each end - one for feeding, the other for hanging on while they feed. They all belong to a group of legless invertebrates (animals without a skeleton) called Annelids - "anulus" is the Latin for "ring". This means that the body is divided into separate segments (which look like rings) connected by a continuous gut, a nerve and a blood vessel. They use external bristles (chaetae) to pull themselves along in a sort of concertina-like motion.
Not all worms are Annelids. Some belong to a group called Nematodes. Many nematodes are internal parasites, often living in the guts of mammals (including humans). Leeches are external parasites.
Habitat
European leeches live in fresh water and damp places. There are a few marine leeches living in the Atlantic Ocean which prey on fishes. They can also be commonly found in tropical rainforest such as the Amazon.
Movement
On the whole leeches do not have bristles, but their flattened body allows them to swim effectively in an undulating way. They lie in wait for a passing animal of the right kind and then home in on it. They can contract their bodies to become short and stubby, or extend them to become long and thin.
Feeding habits
Some leeches are blood-suckers, and attach themselves to the skin of animals at a place where blood vessels are near the surface.The mouth end has sharp jaws to cut through the skin of it host. They inject an anti-clotting substance to stop the blood coagulating (thickening) and feed until they are full. Then they drop off to digest their meal, but the puncture bleeds for a while afterwards.
The horse leech (Haemopis sanguisuga), which can be 30 cm long when extended, does not suck horses' blood, but feeds on earthworms, and decaying flesh.
Medical uses
The medicinal leech was used in medieval times in Europe for certain illnesses because doctors believed that sucking out some of their patient's blood helped them to recover. To do this they would apply a leech or two and let them feed. Surprisingly, leeches have come back into fashion for medical use. The anti-coagulant they secrete into a wound helps to stop a scab forming, preventing the skin from sealing over too quickly. This promotes healing from the inside outwards. This is especially important where very delicate repairs have been made to torn tissue.
Fancy having two or three leeches hidden under your bandages! In films about tropical rainforest adventures the tough guys are always removing leeches from their legs.
Additional reading:
An extract from “A Sanguine Attachment 2000 Years of Leeches in Medicine “ by Roy T Sawyer Managing Director, Biopharm. Encyclopedia Britannica INC.
The leech was indispensable in 19th Century medicine for bloodletting, a practice believed to be a cure for anything from headaches to gout. Leeching was largely abandoned as medical science advanced, only occasionally being called upon to treat bruising and black eyes. However, the medicinal leech is making a comeback in modern medicine thanks in part to the work of Dr. Roy Sawyer, an American scientist who established the world's first leech farm. Based at Hendy near Swansea, South Wales, Biopharm is home to over 50,000 leeches which are supplied to hospitals and research laboratories around the world.
Thousands of patients owe the successful reattachment of body parts to miraculous technological advances in plastic and reconstructive surgery; at least some of these operations might have failed if leeches had not been reintroduced into the operating room. The appendages reattached include fingers, hands, toes, legs, ears, noses and scalps.
The pioneering use of leeches in modern plastic and reconstructive surgery can be attributed to two Slovenian surgeons, M. Derganc and F. Zdravic from Ljubljana who published a paper in the British Journal of Plastic Surgery in 1960 describing leech-assisted tissue flap surgery (in which a flap of skin is freed or rotated from an adjacent body area to cover a defect or injury). These surgeons credit their own use of leeches to a Parisian surgeon, one Philippe-Frédéric, who reported in 1836 that he had used leeches to restore circulation following reconstruction of a nose.
The rationale behind the use of leeches in surgical procedures is fairly straightforward; nonetheless, it is subject to misunderstanding, even by clinicians. The key to success is the exploitation of a unique property of the leech bite, namely, the creation of a puncture wound that bleeds literally for hours. The leech's saliva contains substances that anaesthetise the wound area, dilate the blood vessels to increase blood flow, and prevent the blood from clotting.
Microsurgeons today are adept at reattaching severed body parts, such as fingers. They usually have little trouble attaching the two ends of the arteries, because arteries are thick-walled and relatively easy to suture. The veins, however, are thin-walled and especially difficult to suture, particularly if the tissue is badly damaged. All too often the surgeon can get blood to flow in the reattached arteries but not veins. With the venous circulation severely compromised, the blood going to the reattached finger becomes congested, or stagnant; the reattached portion turns blue and lifeless and is at serious risk of being lost. It is precisely in such cases that leeches are summoned.
Links
- Worm world: Larry Leech - very delightful site for children & adults
- BBC News: Bloodsuckers hit the medical comeback trail
- BBC News: Leeches offer vein hope
- Biopharm Leeches Online Website - Suppliers of Medicinal Leeches since 1812
- Jiskha Homework Help - Science: Biology: Leeches - barebone info without the frills
- Armeniaweek: Treatment that Sucks: Leeches practice medicine at Yerevan center
- Medicinal Uses of Leeches from the Amazon and elsewhere: An Interview with Roy T. Sawyer
- Norman Miller: Science/Health/Medical: Use of leeches...
