Leeches, a parasitic worm species in the subclass Hirunda within the phylum Annelida. Leeches are closely related to earthworms as they have similar soft, segmented, muscular bodies which can contract and lengthen. Leeches are most typically found in shallow waters, where they live hidden in aquatic plants, stones, logs, and debris. Leeches are attracted to disturbances in the water so they will hang around swimming areas and docks, and they are most active during the hot summer, while in winter they hide out in the mud and stay inactive. There are between 700 and 1000 species, with most leeches live in Southeast Asia and Australia. Out of all the species, only one isn’t as common as the others: Hirudo medicinalis.

Hirudo medicinalis is also known as the European medical leech. This species is classified as a “medical leech” because they have been used in medicine since ancient times and even still to this very day. The earliest documented time where leeches were used in medicine was around 1500 BC according to paintings found in ancient Egyptian tombs.

Leech saliva contains the chemical hirudin, which can help prevent blood clots. Blood clots are defined as a gelatinous mass that contains fibrin and blood cells which are formed by the coagulation of blood. Moreover, leech spit also contains calin which is able to keep a wound open for an estimated 12 hours, which can be helpful during surgeries, most commonly reconstruction surgeries and plastic surgery.  This creature’s spit can also  used against diabetes, arthritis, many skin disorders, ear abnormalities, and infectious diseases. Leeches spit is most commonly used in hospitals for preventing blood clots. During a surgery leeves spit will be used to keep the wound open and to prevent blood clots and infection after the surgery. 

The “medical leeches” are still used today, but not as commonly as in ancient times. This is due to the rarity of this species of leeches. There are only 12 species of leeches that are able to be used in medicine, with six of them being poisonous and six that are not.