Getting Close to Leeches
by Randi Lynn Mrvos
Some scientists travel to the humid forests of Madagascar and the hippo-infested waters in Africa to study leeches. Fortunately they don't have to look for longthe researchers find their specimens very "attached" to them. Literally.
Leeches are one of nature's most misunderstood creatures. Though they have a "creepy" reputation, some are quite colorful. The European medical leech is green with red lines on it body that run from the front end to the back end. The North American medicinal leech has black and orange polka dots.
There are over 500 species of leeches. The biggest leech can reach 8 inches long. Leeches are annelids, like earth-worms. They can be found in most parts of the world. Leeches live in fresh water, in sea water, and on the land. Many are nocturnal, meaning they are active at night.
A leech's body is like a stretchy sack that swells to hold food. Some leeches have a pair of eyes. Others have three, four, and even five pairs of eyes. Leeches have suckers at both ends of the body which help them to move. The rear and head suckers take turns gripping a surface, like the way an inchworm crawls along.
Most leeches are parasites. Parasites live and feed on other organisms called hosts. Hosts can include fish, frogs, turtles, and humans as well as other animals. Some leeches cut the skin of the host with three teeth-lined jaws. Other leeches pierce the skin of a host with a proboscis. A proboscis is a muscular tube-like mouth with teeth in the middle of the jaws. Several groups of leeches have no teeth or jaws and shallow their prey whole.
Leech bites can be felt. Contrary to popular belief, leeches don't release an anesthetic substance into the wound to reduce the pain. But when a leech feeds, blood loss is hardly felt (though small hosts may suffer).
After piercing into the skin, the leech attaches its oral sucker to the wound. The leech makes a tight seal around the wound with the muscular outer rim of its mouth. Then it pumps blood into its stomach. Normally, blood clots to close off a wound. But leeches inject a substance called an anti-coagulant into the wound to keep the blood liquid as they suck. When the leech is full, it releases its sucker and drops off.
During medieval times, leeches were applied to patients to suck out the "bad" blood. This medical practice was most popular in the 1830's. As recent as 2004, leech therapy has been approved for medical use. While it has been reported that leeches can help people with osteoarthritis, those studies were questionable. But, leeches can help to rebuild skin lost to cancer. Leeches also help in the reattachment of severed fingers by removing excess blood and improving blood circulation.
Researchers want to understand the host and habitat choices of leeches as well as their feeding behavior. They also want to better understand the species for medicinal value. So they search for specimenssometimes hiking barefooted and wearing shortsretrieving them from their legs and feet. Researchers know it's a tempting way to catch these clingy guests.
The author wishes to thank Dr. Mark E. Siddall, Curator Division of Invertebrate Zoology AMNH and leech biologist for his expertise.
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Randi is a columnist for The Creativity Connection, an editor for the educational website www.Viatouch.com , and a former consultant for Pearson Digital Learning. She writes for children's, parenting, and writers' publications. Her publishing credits include Byline, Mothering, The Christian Science Monitor, Highlights for Children, Know, Nature Friend, and Learning through History Magazine.