Any of various worms that live in water and suck blood from other animals, including humans. One species, the medicinal leech, has been used in bloodletting and in helping to heal wounds and surgical grafts. Leeches are annelids, related to earthworms. Leech: a person who is supported by or seeks support from another without making an adequate return. Synonyms: bloodsucker, freeloader, free rider Find the right word.
Poor leeches. They get a bad reputation for being nothing but slimy, oozy, hysterics-worthy bloodsuckers—and while they may be all those things, leeches are actually pretty cool once you get to know them.
From a distance. On dry land. Not stuck all over your legs.
Here are a few things you might not have know about these creepy crawlies.
1. Leeches are actually worms
Yup. Leeches have a lot in common with your everyday earthworm—but there are some important differences. Leeches’ bodies are much more solid than earthworms’, and while they show some external segmentation, the divisions on the outside don’t match up with how organs are arranged on the inside. Plus, there’s that whole bloodsucking thing. But, like earthworms, leeches make great bait, especially for walleye.
2. Not all leeches suck blood
Blood-eating leeches are only one type, although they’re the ones we most often notice, mostly as we’re dancing around trying to rip them off our legs. Many freshwater leeches, in fact, don’t eat blood at all—they’re carnivores, but they stick to molluscs, insect larvae, and worms. Even those that do drink blood aren’t actively looking for human blood—they prefer frogs, snails, turtles, and other aquatic creatures. But hey—a meal’s a meal, and if someone’s ankle presents itself, it’s nom time.
3. Leeches are hermaphrodites
Leeches have both male and female reproductive organs, but that doesn’t mean they can do it all themselves, fertilization-wise. Instead, leeches line themselves up, head to feet—or as close as a leech gets to a head, or feet—and trade sperm packets. Not quite a romantic weekend in Niagara Falls, but it does the trick.
4. Leeches are everywhere
You’re never going to escape them, so you might as well learn to appreciate them. Leeches are found on pretty much every continent—and while there are no freshwater leeches in Antarctica, you can find the little suckers floating in every ocean in the world.
5. Leeches can get really big
One species found in the Amazon can grow up to 45 centimetres long—with a proboscis (nose) that can grow up to half a foot in length. Fortunately, most of the species found in Canada aren’t quite so horrifyingly massive—the bloodsucking species we’re familiar with, Macrobdella decora, only grows up to 10 cm or so.
6. Leeches are used in medicine
No, not for old-fashioned bloodletting—that went out of style with the corset and the bustle. Instead, doctors use leeches and their blood-clot-busting saliva to help drain blood from swollen areas following reconstructive surgery—especially small areas with lots of blood vessels like ears, fingers, and toes, where blood clots can easily form. And although the science is still a little fuzzy, researchers in Germany are also using leeches to help with the pain of osteoarthritis.
7. Leeches can’t hear, and they don’t see much
Leeches don’t have ears, although they can sense vibrations through their skin, and they can’t see much beyond how bright a light is. Instead, they use a strong sense of taste and touch to communicate chemically and physically with each other.
8. Leeches adapt well to tough conditions
Some species can go a year without food, and they tend to tolerate low levels of oxygen well. Also, some species seem to do just fine in areas with high levels of pollution.
9. If a leech is stuck to you, just wait it out
If you get out of the water and you’ve got a leech stuck to you, the best—although not the easiest—thing to do is simply wait for it to finish eating, at which point it will drop off and go on its merry way. If you can’t get over the ick factor, though, a little salt sprinkled on the leech will cause it enough discomfort to get it to drop off early.
10. Leeches eat a lot, relatively speaking
You’re definitely not going to die from a leech bite, but they are capable of eating up to five times their body weight in blood. Conveniently, they can store excess nutrients for later use, just in case pickings get slim in the blood department.
by Jay W. Sharp
As you would probably expect, you stand a far higher chance of coming face to face with a leech if you hike a tropical rain forest or tow Humphrey Bogart's African Queen than if you explore our Southwest desert basins and mountain ranges. You may be surprised to discover, however, that you can find a respectable community of leeches, including blood sucking species, in locations such as our quiet river basin wetlands and high country ponds.
For example, in Montezuma Well, a pond in a geologically distinctive setting in the Sonoran Desert north of Phoenix, 'Blood sucking leeches are…abundant in the aquatic vegetation,' according to the National Park Service in its Internet site. Other species are even more abundant.
Meet the Leech
Worldwide, somewhere between 700 and 1000 species populate freshwater, saltwater, estuarine and moist land ecosystems, said leading authorities Fredric R. Govedich and Bonnie A. Bain in the All About Leeches Internet site. About 10 percent of the species occur in the United States.
Related to earthworms, leeches tend to have a colorful, tear-drop-shaped, flattened and segmented body, ranging in length from less than an inch to several inches in length. They have suckers on the underside of each end of their body—an oral sucker at the forward (narrower) end and a second sucker at the rear end. They have, on the head and body, sensory organs that enable them to detect light, odors, vibrations and temperature variations.
In water, leeches swim with an undulating motion, something like eels. On solid surfaces, they move 'by alternately attaching and detaching [their] suckers, crawling about in a looping inchworm like motion,' said Govedich and Bain.
Leeches
The leeches, all with their mouth parts centered in their forward suckers, comprise three kinds of carnivores. One kind – the 'engulfer,' which has no teeth or jaws – feeds on small invertebrates, swallowing prey whole. A second kind – equipped with a hollow needle-like proboscis – spears the flesh of worms and snails, secretes an anticoagulant into the tissue to assure the free flow of blood, and sucks out the juices of prey. The third kind – the parasitical blood sucker, which has jaws and razor-sharp teeth – bites into prey, including amphibians, reptiles, fish, waterfowl, mammals and – given the opportunity – human beings. Using both the forward and rear suckers to remain attached to its host, the toothed blood sucker excretes a mucous that, along with suction, fixes it in place while it feeds. It releases an anesthetic to numb the wound site. It secretes an anticoagulant into the wound. If left undisturbed, it will ingest several times its weight in blood. Engorged, it releases its hold and drops off, seeking out a quiet dark refuge to digest its meal, a process that may last for several months. While all leeches are predators, they also serve as prey for fish, waterfowl, reptiles, large aquatic insects and even other leeches.
Historically, possibly since the Stone Age, leeches have played medicinal roles. According to the BBC Internet site, leeches served Egyptians, Persians, Greeks, Chinese and other early civilizations in bloodletting ceremonies with purposes such as sucking out evil spirits from one's body.
After falling out of favor for most of the 20th century, leeches have returned to the medical scene, providing anticoagulants and anesthetics for micro- and reconstructive surgery and, possibly, in the future, heart attack and stroke treatments.
Biology of the Leech
Any two leeches of the same species can mate because all have both male and female sex organs. That is, they are 'hermaphrodites,' like earthworms. In mating, two leeches entwine their bodies and deliver sperm into each other. 'The sperm,' said Govedich and Bain, 'are then transported to the eggs where fertilization occurs.'
The leech deposits its eggs in a gelatinous cocoon. While there is considerable variability among species, a typical leech may attach the cocoon to submerged plant material or to a stone surface. The cocoon is so tough that it will survive passage through the digestive track of a waterfowl. After several weeks or months, the eggs hatch, and the young emerge, looking like diminutive adult leeches.
Surprisingly, many leech species make excellent parents, according to Govedich and Bain. A leech may care for its young 'in a manner that resembles the care shown by birds or even mammals.' It may build a nest for its brood. It may carry its brood attached to its under side or quartered in an internal, marsupial-like pouch. It may even capture and kill prey for its babies until they can provide for themselves. The leech dies after one or two reproduction cycles.
Attack of the Blood Suckers
According to the Field Guide to Venomous and Medically Important Invertebrates Affecting Military Operations, 'When a person enters leech-infested habitats, the leeches quickly swim toward the source of the water disturbance.' A leech will quickly attach to the skin with one of its suckers. It explores the body in its inchworm style until it finds its choice site for a meal, for instance, at the toes or along the shin. It quickly perforates the skin and begins to feed. After it releases its hold, engorged, the wound may continue to bleed, a result of the anticoagulant, for an hour or more.
According to a horror story on the BBC Internet site, leeches in unfiltered and untreated water drunk by Napoleons' soldiers operating in the Syrian Desert in 1799 attached themselves to the men's noses, mouths and throats. As they filled with blood, they caused some soldiers to die of suffocation and others of blood loss.
Fortunately, leeches raise comparatively small risk in the Southwest. (After all, we filter and treat our water.) While repulsive, the bites tend to be small and inconsequential, especially if you remove the leech and treat the wound properly. (See Removing Leeches and Treating Leech Bites for more information.)
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