Hirudo medicinalis
ORDER
Arhynchobdellae
FAMILY
Hirudinidae
TAXONOMY
Hirudo medicinalis Linnaeus, 1758.
OTHER COMMON NAMES
French: Sangsue médicinale; German: Medizinische Blutegel; Italian: Sanguisuga; Spanish: Sanguijuela medicinal; Swedish: Medicinsk blodigel.
PHYSICAL CHARACTERISTICS
Intricate red and green patterning on dorsum (upper surface), yellow medial lines, and tan venter (belly). Commonly grows up to 3.9 in (10 cm) or more in length and 0.39 in (1 cm) wide. Parabolic arc of 10 cephalic eyes arranged in five pairs. Three jaws in pharynx with fine denticles (small toothlike structures).
DISTRIBUTION
British Isles, southern Scandinavia, continental Europe eastward to the Urals and to western Turkey. Distribution is very irregular and patchy as of 2003.
HABITAT
Found in naturally occurring freshwater lakes, ponds, streams, and marshes. Usually rests at air/water interface near shore.
BEHAVIOR
An excellent and agile swimmer, this leech can detect and move toward disturbances in the water from a distance of some yards. Vertical wavelike motions and use of the caudal sucker provide forward movement and thrust. Applies negative pressure to surfaces with its oral and caudal suckers for suction and attachment purposes.
FEEDING ECOLOGY AND DIET
Feeds principally on the blood of amphibians and fishes; occasionally feeds on mammals. Creates a three-part incision with its jaws and uses negative pressure of pharynx to draw out the upwelling blood. Can ingest quantities of blood several times greater than its unfed body weight. Can store blood in crop (enlarged area at the base of the esophagus) for months.
REPRODUCTIVE BIOLOGY
Mating takes place through gonopore-to-gonopore copulation involving an eversible penis and vaginal pouch. The eggs are laid in clitellar secretions surrounding the body, which are then slipped over the head to form a protective egg case or cocoon. Cocoons with approximately 10 eggs each are deposited on land near the edge of a body of water. Development is direct.
CONSERVATION STATUS
Overexploited; has seen its natural habitat become fragmented and highly restricted. Listed as Lower Risk/Near Threatened by the IUCN; also listed in CITES Appendix II.
SIGNIFICANCE TO HUMANS
Used medicinally for the purpose of phlebotomy (drawing blood) for millennia, and popularized for this use in the nineteenth century. Most historical uses are of dubious utility. Current use in microsurgery to reduce postoperative hematomas is quite legitimate and effective. Commercially available for medical purposes. Several anticoagulants, such as the antithrombin compound hirudin, have been extracted from salivary tissues and have biomedical/pharmacological use. Occasionally featured in motion pictures (e.g., Speed 2).
