The leech is an aquatic worm with a flattened body, which ends at the end of the circular flattened disc, the obstacle being two times larger. It swims with a vertical undulating motion and moves when it comes out of the water with the help of these discs or suction cups, flattening first one on one and then the other and alternately stretching its body. The mouth is located in the center of the anterior disc and is provided with 3 jaws in the shape of a cartilaginous lens. These jaws are lined at their edges with fine, sharp teeth and meet so as to make a triangular incision in the flesh. The head has small high points, assumed by some to be eyes.
The leech belongs to the kingdom (Animalia); Filiu (Annelida); Class (Hirudinea); Order (Gnathobdellida); Family (Hirudidae). The licorice can ingest an amount of blood close to eight times its own weight. Leeches can be found mainly in freshwater lakes, ponds or rivers between 5 cm and almost 25 cm. Leeches are hermaphroditic with both male and female parts, but still need to meet to multiply. After mating, 15-50 eggs are laid in a spongy case or cocoon above the water line often under rocks.
Leech eggs hatch in 3 to 5 weeks, and young leeches need two seasons of feeding before they are ready to reproduce. There are about 45 species of leeches belonging to 22 genera. However, the species commonly cultivated for medicinal use are Hirudinaria granulosa and Hirudo medicinalis. H. granulosa is found in abundance in the state of Madras, Kerala, M.P., U.P. and Punjab, while Hirudo medicinalis is commonly used in the Western world. Leeches are known by the following vernacular names: Alaq (Arabic); Zalu (Persian); Jonk (Urdu); Salook (Turkish); Leech (English); Hirudo (Latin); Bdella (Greek); Jaluka (Sanskrit); Jalu (Hindi); Jalagalu (Telugu); Attai (Tamil); Jiganey (Kannada)