Species Fact Profile: Medicinal Leech (Hirudo medicinalis)

                                                       (European) Medicinal Leech

Hirudo medicinalis (Linnaeus, 1758)

Range: Temperate Europe (including United Kingdom), Central Asia

Habitat: Muddy Freshwater Streams and Pools, Wet Vegetated Ditches

Diet: Blood

Social Grouping: Often found in groups, but asocial 

Reproduction:  Hermaphrodites, reproducing sexually.  Lay approximately 50 eggs near (not in) the water.  No parental care invested

Lifespan: 2-8 Years

Conservation Status: IUCN  Near Threatened

• Grow up to 20 centimeters long.  Tube-shaped body with a sucker at each end.  The anterior sucker, which has "teeth" (about 100 sharp edges), is primarily used for the feeding, while the posterior one mostly aids in leverage and climbing
• Color is brown or green, darker on the dorsal side and lighter on the ventral, often with a thin red stripe on the dorsal side
• Feed by piercing the skin with the teeth of the front sucker, then sucking out blood while injecting anticoagulants (called hirudin) into the wound to keep the blood flowing.  The saliva contains an anesthetic so that the bitten animal does not feel pain during the feeding
• A large leech can consumer up to 10 times its body weight in blood during a feeding, and may not need to eat again for a year
• This species has been used for thousands of years in medicine, both human and veterinary.  Traditionally it was used to restore balance between the "humors", but also to remove access blood, reduce inflammation, and, in more contemporary times, assist with skin grafts and transplants.
• Leeches are still used in a reduced capacity in modern medicine, though it is now far more common to use a synthetic version of hirudin, or devices which are called "mechanical leeches"
• Have declined in recent years, first through over-collection for medicinal use, later through the decline of their favored hosts (horses, which were replaced by cars and tractors) and loss of habitat

Zookeeper's Journal: I have only ever seen a single exhibit of leeches, the tank above, which I photographed at the Oglebay's Good Zoo in Wheeling, West Virginia.  It's been years since I've been there so I don't know if it is still present, and I'm kicking myself for not getting a better picture of the little guys while I was there.  It struck me as one of the coolest, most unique, and yet simplest exhibits of an invertebrate that I'd ever seen.  Few animals inspire more fear and revulsion among humans, while still having such as a fascinating history with us - the medicinal role that leeches have still has implications to this day.  It also takes astonishingly little work to maintain them - in case you were wondering, in captivity they can be fed just a tiny piece of raw liver every now and then.  I would definitely incorporate these fascinating creepy-crawlers, which I had no idea were becoming so rare, in an exhibit on invertebrates (alongside their close relatives, the earthworms) or on human-animal interactions.  There is a lot that could be done with the later kind of exhibit - consider the designated leech receptacle above, which I photographed at the New Orleans Pharmacy Museum.