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Not all leeches are lecherous

July 1, 1993

Not all leeches are lecherous

By Robert A. Hedeen, Naturalist

Does the very thought of a leech make your skin crawl? It probably does if you are imagining a slimy worm attached to your body and feasting on your blood. Yet, while most people recoil at the thought of a leech, some of these cousins of the earthworm were thought to be of great medicinal value in the past, and, in recent years, the scientific justification of their use in medicine has emerged.

A few years ago, a friend and I were seining minnows for bait in a slow moving stream on the eastern shore of Maryland, and when we brought the seine to shore, I was horrified to find a plump leech attached to my abdomen. I immediately grabbed the worm with my fingers and attempted to pull it free, but the creature was so slippery with mucous that this proved to be impossible. I finally was able to dislodge it by scraping its sucking mouth free with the aid of a sharp knife blade. Blood flowed freely from the characteristicY-shaped wound made by the leech’s three blade-like teeth, and at least a half hour passed before the blood clotted.

When a leech decides to take a blood meal from an unsuspecting victim, it attaches to the prey with its strong suction cup-like mouth. Salivary secretions that are anesthetic in nature are injected into the cuts made by the teeth, and the victim is unaware he is being attacked. The leech saliva also contains a powerful blood anti-coagulant known as hirudin. The leech may require considerable time to fill its large stomach, and the hirudin prevents the blood from clotting and interfering with the feeding process. Other animals such as mosquitoes and other blood-sucking flies, ticks, mites, and fleas also inject an anti-coagulant when imbibing our blood, but their clot preventer is not as potent as that of the leech.

For almost as long as the art of medicine has been practiced, descriptions of the use of leeches as a method of painless bloodletting have been described. The probable earliest documented use of leeches by physicians is from early Egypt. A wall painting was discovered in a tomb dating to the 18th dynasty (1567-1308 B.C.) and depicts the application of a leech to a human by a physician or barber (one in the same in those days).

By the early 17th century, the medicinal leech was widely used in Europe, reaching a peak in France in the first half of the 19th century. Medicos must have thought them to be very affective, as leeches were in every hospital. Import duty records confirm this as more than one billion leeches were brought into the country during the 19th century.

In the heyday of “leeching,” from about 1820-1850, leeches were the aspirin of the day. They were routinely used to treat almost any ailment: obesity, mental illness, tumors, gout, whooping cough, insomnia, and headaches, to name a few. For headaches, leeches were attached to each side of the head. It was believed that somehow the worm extracted “bad blood” from the patient and replaced it with “good blood.”

The most common use of leeches in this country was cosmetic in nature, and they were primarily employed to treat bruises and black eyes. This treatment is probably available today in a barbershop in an ethnic neighborhood in Chicago or other large city.

The anti-coagulant hirudin is finding usage in modern medicine, and it may well be that this component of the leech’s saliva will be to cardiovascular disease what penicillin was to bacterial disease.

Leeches abound in lakes, ponds, and sluggish streams, and more than 45 species of them have been recorded from all parts of the United States. In some areas, populations of more than 700 leeches per square meter have been reported, but they are usually not so numerous.

Fortunately for man and some other animals, not all leeches have the blood-sucking habit. Many exist as commensals in association with hosts that are not harmed by their presence. In the case of the crayfish leech, the worms hang on to the crustacean’s outer suit of armor and feed on scraps of food discarded by their host.

Another beneficial use of the leech is as an extraordinary fish bait. I once caught a six-pound largemouth bass from a river in Texas using a leech as bait. No other lure, natural or artificial, attracted any other type of fish’s attention that memorable day.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960-1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

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