Leech therapy, more scientifically known as hirudotherapy, has been practiced for ages. Evidence suggests that doctors in ancient Egypt used leeches to treat certain ailments. Though the idea of curing illnesses by general bloodletting has been abandoned, the practice of applying leeches is still surprisingly common. They are mainly used to treat a variety of vein-related problems (by draining internal bleeding until veins have time to heal). In some schools of medicine, leeches are applied to relieve the symptoms of chronic illnesses like arthritis.
Special medicinal leeches are used in hirudotherapy. Though doctors bought wild-caught leeches from professional leech collectors in the past, the blood suckers are now grown and kept in laboratory-like settings until they are needed. Keeping the invertebrates in sterile conditions is important for leech growers, but the creatures themselves are quite hardy. When kept in cold (40 degrees) temperatures, leeches will need to feed only once every few years.