They are commonly found in lakes and ponds and many of them provide food for vertebrates such as fish, ducks, turtles and some other birds. But before we talk about them feeding on us, let's look at some of the cool things they have been used for. Leeches may seem slimy, but they are being used for a wide variety of scientific and engineering advances. For about 2500 years, leeches were needlessly applied for many ailments. They were a cure-all that didn't cure much.
Today there are actually clinical applications of leeches.
The small leech Hirudo medicinalis is particularly valuable for plastic and reconstructive surgery. The leech can also remove any congested blood to allow normal circulation to return to the tissues and prevent gangrene from setting in. Leeches may also be used to treat black eyes. And hirudin, the anticoagulant, may be used in the treatment of inflammation of the middle ear. Hirudin may also eventually be used in invitro blood sampling.