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When you think of leeches, you probably don't get warm fuzzy feelings. Most people recoil at the thought of a leech attaching itself to a leg while swimming. Well, it's true that leeches are kind of gross, but they are pretty harmless. On this page we hope to provide all sorts of information to help give leeches a slightly more respectable name.

Summertime means more leeches

Did you know!?

Some leeches will even feed on other sanguivorous (blood sucking) leeches!

It's true: 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).

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

Did you know!?

Barbers were once responsible for treating patients with leeches—the red stripes on barber poles symbolize bloodletting.

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 (external link)!

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.

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

Did you know!?

Studies show that the cocoons are capable of surviving the digestive system of a duck.

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 fertilized eggs are deposited in a tough gelatinous cocoon that is secreted by the clitellum and contains nutrients for the developing leeches. The cocoon is either buried in mud or affixed to submerged objects, and after several weeks or months the young emerge as small copies of the adults. In the family Glossiphoniidae, many species of leeches attach the cocoons directly to the ventral side of the parent. The parent is able to protect the young as they develop and provide prey for the young leeches after they hatch. Adult leeches die after they reproduce one or two times.

Underwater leech photo

Leech Link(s)

More interesting info about leeches:

Biopharm suppliers of medicinal leeches since 1812

For questions about information on this page, please contact Kate O'Laughlin, Ecologist.