Guillaume van den Bossche, 1639
Ancient Indian, Greek and Egyptian texts indicate that these segmented worms have been used to treat everything from flatulence to joint pain for nearly 3,000 years. The medieval practice of bloodletting was perhaps the most infamous use of the vampire-like worm. Doctors believed an imbalance of blood, phlegm, black bile, and yellow bile was the cause of most ailments. Leeches were applied to patients believed to have an excess of blood. While the medical community no longer accepts the widespread use of bloodletting, research has shown proteins in leech saliva can help treat cardiovascular problems, cancer, metastasis, and infectious diseases.