Introduction to Leeches
Leeches are annelids - segmented worms - related to the common earthworm. There are 650 known varieties of leeches, ranging from tiny to 18 inches long. There are freshwater, terrestrial, and marine leeches. Some types of leeches feed on insects and small worms, others are parasites that feed on the blood of fish or mammals.
Bloodsucking leeches use both mechanoreception (vibratory/touch) and chemoreception (smell/taste) to located food. Their eyes located at their anterior end can only detect changes in light intensity and possibly some movement. The searching action observed when a leech is being attached for medical therapy is simply the leech tracking prey. "Sniffing" for food, so to speak. After attaching, the method of blood feeding depends upon the species. Bloodfeeding methods vary from tiny serrated jaws to a three inch filamentous probosis.
There are 3 species currently used for various medical purposes: Hirudo medicinalis, the European medicinal leech; Hirudinaria manillensis, the Asian medicinal leech, and Haementeria ghilianii, the Amazon leech. Compared to the other medical leeches, Hirudo medicinalis is relatively small, 1 to 2 inches long before feeding. The Hirudo medicinalis is remarkably well-equipped for bloodsucking. H. medicinalis' mouth has 3 jaws and hundreds of tiny teeth, leaving a bite mark that resembles a Mercedes-Benz symbol. Hirudo medicinalis is the only FDA approved leech and is the most commonly used in plastic and reconstructive surgery.
FDA approved medicinal leeches are raised in special facilities, specifically for medicinal purposes. Roy Sawyer, an American researcher, recognized the medical value of leech therapy and started one of the world's first modern leech farms, Biopharm, based in Wales, UK. Biopharm keeps leeches in tanks, waiting to be shipped around the world to laboratories and hospitals.
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