What are leeches?
Let's not be too tough on the leech, after all, leeches can save human lives! Chemicals from the leech fight germs, widen veins, and restore blood circulation. Doctors are experimenting with leech saliva, a substance that keeps blood flowing freely and prevents clotting in people. This chemical may prevent blood clots that could travel to the heart and cause death.
But leeches bite and suck people's blood! When a leech attaches itself to you in the lake, you aren't looking for a medical cure, so you'll want to remove it. Why do they pick on you? Leeches may sense the ripples in the water and then swim on over. (Just for the record, only a few species prey on people.) Some leeches have 80 saw-like teeth. Their bite leaves a clear Y-shaped mark. Others suck blood through a straw-like body part called a proboscis. A leech can suck up to ten times its weight in blood in about 30 minutes. When it's full, it drops off.
These vampires of the worm world also live just about anywhere that gets damp. High mountains, polar seas, desert water holes, you name it! Some leeches can bite through a hippo's hide, while others live on the gums of the Nile crocodile. In the U.S., leeches mainly latch onto people who are swimming or playing in ponds and lakes.
With its slimy, squirmy, wormy body, a leech will never win any beauty contests, but they do have their good side.