---

Leeches are more abundant during the summer. They reproduce in the spring, and the young leeches are out of their cocoons several weeks later (summertime!). Leeches grow for a season, and are ready to breed by the following spring to begin the cycle again. They are commonly found in lakes and ponds and many of them provide food for vertebrates such as fish, ducks, turtles and some other birds. Leeches tend to swim near the substrate to avoid risk of predation, and they usually stay near the shallow regions of their aquatic habitats (hmmm...shallow and substrate sounds like where most human feet are walking in the water). Did you know!? Some leeches will even feed on other sanguivorous (blood sucking) leeches!  Leeches prefer invertebrates and other vertebrate hosts (fish, reptiles, and mammals) to humans, but if a human is around, some of them will climb on for a meal. But before we talk about them feeding on us, let's look at some of the cool things they have been used for. The Value of a Leech  Leeches do provide food for all sorts of critters—a very valuable trait indeed. And on top of that, what could be a more respectable job for a leech than helping the advancement of science and technology? Leeches may seem slimy, but they are being used for a wide variety of scientific and engineering advances. For about 2500 years, leeches were needlessly applied for many ailments. They were a cure-all that didn't cure much. Today there are actually clinical applications of leeches. For example, in 1985 microsurgeons in a Boston hospital used leeches when they had to reattach a little boy's ear that had been bitten off by a dog! (Click here for the story.) The small leech Hirudo medicinalis is particularly valuable for plastic and reconstructive surgery. This leech produces several important substances that make its bite very special, including an anticoagulant (hirudin), a local vasodilator, and a local anaesthetic. These substances allow continued bleeding that mimics venous circulation for up to 10 hours after the leech has detached (and the anaesthetic makes the bite painless). The leech can also remove any congested blood to allow normal circulation to return to the tissues and prevent gangrene from setting in. Did you know?! Barbers were once responsible for treating patients with leeches—the red stripes on barber poles symbolize bloodletting.  Leeches may also be used to treat black eyes. And hirudin, the anticoagulant, may be used in the treatment of inflammation of the middle ear. Hirudin may also eventually be used in invitro blood sampling. Researchers have found that the anticoagulant and clot-digesting properties of substances in leech saliva make them potentially useful for the treatment of heart attacks and strokes. No leeches have to be harmed in the making of these drugs! The leeches can be "milked" for their secretions without being harmed. Plus, researchers are looking into the possibility of synthetically engineering leech saliva to be used for all these purposes. Links to leech studies (those valuable leeches!):  Effect of ale, garlic, and soured cream on the appetite of leeches      Feeding (and not just on your leg!)  Did you know?! Sanguivorous leeches can ingest several times their own weight in blood at one meal.  Like vampires, most leeches feed by sucking blood from their hosts (they are sanguivorous). They generally attach themselves to their meal with their anterior sucker, and some have a proboscis they insert into their prey from their mouth. Others may use strong jaws to cut into through the tissues of their prey. A third type of leech doesn't have jaws, so it must feed by swallowing small prey items whole. Reproduction Like worms, leeches are hermaphroditic (also called monoecious)—they have both male and female sexual organs. Leeches can only reproduce sexually, and unlike some worms, they are not capable of regeneration. Like earthworms, they have a clitellum, which is a region of thickened skin that in leeches is only obvious during the reproductive period. Mating typically involves the intertwining of bodies where each leech deposits sperm in the others' clitellar area. The sperm then make their way to the ovaries for fertilization.

The Practice of Leeching Throughout History

---

The use of leeches in medicine dates as far back as 2,500 years ago when they were used for bloodletting in ancient Egypt. All ancient civilizations practiced bloodletting including Indian and Greek civilizations. In ancient Greek history, bloodletting was practiced according to the humoral theory, which proposed that when the four humors, blood, phlegm, black and yellow bile in the human body were in balance, good health was guaranteed. An unbalance in the proportions of these humors was believed to be the cause of ill health. Records of this theory were found in the Greek philosopher Hippocrates’ collection in the fifth century B.C. Bloodletting using leeches was one method used by physicians to balance the humors and to rid the body of the plethora. In medieval Europe, a number of superstitious ideas and religious philosophies started to influence the practice of bloodletting. The practice continued on up until the 19th century. In 1833, bloodletting became so popular in Europe, that the commercial trade in leeches became a major industry. France, suffering a deficiency, had to import 41.5 million leeches. The medicinal leech almost became extinct in Europe due to the extremely high demand for them. Leeches were collected in a particularly creepy way. Leech collectors would wade in leech infested waters allowing the leeches to attach themselves to the collector’s legs. In this way as many as 2,500 leeches could be gathered per day. When the numbers became insufficient, the French and Germans started the practice of leech farming. Elderly horses were used as leech feed where they would be sent into the water and would later die of blood loss. Leeches were thought to be able to cure everything from headaches to brain congestion. They were used to cure obesity, hemorrhoids, nephritis, laryngitis, eye disorders as well as mental illness. Their use continued on until the 1960s when their use in medicine was discontinued. Leeches in Modern Medicine The use of leeches in medicine, otherwise known as Hirudotherapy, made its comeback in the 1980s after years of decline, with the advent of microsurgery such as plastic and reconstructive surgeries. In operations such as these, one of the biggest problems that arises is venous congestion due to inefficient venous drainage. This condition is known as venous insufficiency. If this congestion is not cleared up quickly, the blood will clot and arteries that bring the tissues their necessary nourishment will become plugged and the tissues will die. It is here where the leeches come in handy. After being applied to the required site, they suck the excess blood, reducing the swelling in the tissues and promoting healing by allowing fresh, oxygenated blood to reach the area until normal circulation can be restored. The leeches also secrete an anticoagulant (known as hirudin) that prevents the clotting of the blood. The leech’s saliva is truly extraordinary containing a number of chemical compounds useful in medicine. These include a local anesthetic that the leech uses to avoid detection by the host, the anti-coagulant hirudin that can help prevent heart attacks and strokes, a vasodilator and a prostaglandin that help reduce swelling. The leech’s gut harbors a bacterium known as Aeromonan hydrophila. This bacterium aids in the digestion of ingested blood and produces an antibiotic that kills other bacteria that may cause putrefaction. Not only are leeches economically beneficial costing as little as $4.75 to $6.50 apiece, but studies have shown that Hirudotherapy doubles the success rate of transplanted tissue flaps. This is a much higher success rate than that brought on by drugs or further surgery. Hirudotherapy has proven to be useful for a number of other conditions including cardiovascular disease, ophthalmology and dermatology. Hirudin is also used in the treatment of inflammation of the middle ear. Osteoarthritis, which is a painful condition of the knee, is also thought to benefit from leeching. Studies performed by researchers from the Essen-Mitte Clinic in Germany have shown that when leeches were applied to the knees of patients with osteoarthritis, they helped to alleviate the inflammation and pain associated with the condition. The hazards associated with leech therapy include infection, excess blood loss that may require blood transfusion, the loss of leeches in body orifices and spaces, and allergic reactions. Some patients find the use of leeches disgusting, which makes it necessary that they have basic information on the benefit of leeches before the procedure. The secretion of a local anesthetic by the leech makes the procedure painless except for the initial attachment phase. They fall off promptly after they have completed feeding. Scientists at the University of Wisconsin-Madison have developed a mechanical leech as an alternative to real leeches. The synthetic leech mimics the action of the leech allowing for fresh blood to flow through the wound, but unlike the leech, it is insatiable and can continue to remove blood for as long as is needed whereas the leech only feeds for about half an hour.

Nasal leeches are often visible infesting external nasal passages and also infest the nasal sinuses.