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How to Identify Leeches

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Many people wince at the thought of leeches: dark, wriggling blood-suckers chewing away at swollen flesh. While it's true that leeches can occasionally seem gruesome (some are big and strong enough to bite through the skin of a hippo, while others make their homes in the nooks and crannies of crocodile gum lines), for the most part, they're relatively harmless. Still, humans can't guarantee an escape from these infamously vampiric and often misunderstood animals.


Leeches are wide, flat, segmented worms that carry suction cup-like appendages at each end of their bodies. These animals can grow anywhere between a few millimeters to almost 10 inches in length. They come in dark hues -- black, brown and sometimes green -- and can feature spots or stripes or no markings at all. Many varieties have visible pairs of eyes perched atop their front ends. Those species that consume blood or animal tissue can have mouthfuls of up to 80 saw-like teeth or powerful vice-like jaws.


The majority of leech varieties live in shallow, slow-moving or relatively stagnant freshwaters. Others can be found in oceans, marshlands, or soppy-wet soils. Although these animals prefer to feed on fish, in the United States most people come into contact with leeches while splashing around in their favorite swimming holes, ponds or lakes. Here, they sometimes latch onto human skin and proceed to suck their hosts' blood.

Feeding Behavior

Many varieties of leeches are predatory, consuming worms, aquatic insects, snails and other invertebrates. Leeches that feed on blood alone produce a special kind of saliva that prevents the formation of blood clots, allowing a steady stream of blood to flow as long as a leech is hungry. Once a leech attaches itself to a host, it can draw up to 10 times its own body weight in less than half an hour. Once it's sated, it simply drops away.

Reproduction and Growth

Most leeches carry both male and female sex organs, allowing a single leech to both lay and inseminate eggs. These eggs are contained in cocoons and attached to plant matter, damp soil, underwater debris or even the bodies of the parents that laid them. Once hatched, offspring look like miniature versions of their adult parents.The only change they undergo as they age is an increase in size. In fact, depending on temperature and the availability of food, most leeches can reach maturity within a few weeks or months.