Quick Take
- There are between 700 and 1,000 species of leeches
- Leeches are primarily ectoparasitic, living and feeding on the outside of a host’s body, though a few species can attach to internal mucous membranes.
- Ectoparasitic leeches are still used in medical settings.
Leeches are worm-like creatures that live in water and belong to the phylum Annelida and the subclass Hirudinea. Many leeches are parasites that feed on the blood of humans or other animals, but some species are predatory and feed on small invertebrates. Leeches have soft, muscular, segmented bodies that can lengthen and shrink, similar to earthworms, making their bodies appear elastic. While there are between 700 and 1000 different species of leeches, most are not dangerous to humans. However, some hazardous species can attach to internal mucosal surfaces (such as nasal cavities) or cause significant blood loss. Continue reading to learn more about the most dangerous leeches.
Leeches: Overview
Unlike earthworms and other segmented worms, which add segments throughout their lives, leeches hatch with a fixed number of segments. ‘Leeches have a fixed number of 34 segments, and each segment is divided into a set number of rings (annuli) that do not change as the leech grows. Almost all leech species possess two suckers: one at the anterior (front) end and one at the posterior (back) end. The posterior sucker is used for adhesion, while the smaller anterior sucker surrounds the mouth for feeding.
The giant Amazonian leech (Haementeria ghilianii) feeds on the blood of aquatic mammals, turtles, and fish, using its long proboscis to pierce the skin like a hypodermic needle rather than using biting jaws.
Which Leeches are Dangerous?
Leeches in the Praobdellidae family are considered among the most dangerous to humans and other mammals because of their habit of invading and feeding on internal mucous membranes. While most leeches are external parasites, Praobdellids are endoparasitic,
entering the body through orifices, and typically attach to the nose and throat, which can lead to severe anemia, airway obstruction, and, in extreme cases, death.
As hematophagous (blood-feeding) parasites, these leeches produce a variety of anticoagulants and bioactive proteins in their saliva to inhibit blood clotting in the host, ensuring efficient feeding. The most common sources of infection are drinking unfiltered, contaminated water or swimming or bathing in infested water.
At between two and three inches long, the tyrant leech king (Tyrannobdella rex) is not among the world’s largest leeches, but it is considered one of the most dangerous. Found primarily in the upper Amazon region of Peru, the tyrant leech king attaches itself to mammalian mucous membranes, including those in the nose and mouth. The species was officially recognized in 2010 after it was discovered and removed from the nose of a nine-year-old girl in Peru in 2007.
Which Leeches are Helpful?
One of the most well-known species, the European medicinal leech (Hirudo medicinalis), gained a reputation for its healing abilities in the 19th century. However, the use of medicinal leeches plummeted in the early 20th century before experiencing a resurgence in the 1970s. Currently, medicinal leeches are used in plastic and reconstructive surgery to relieve venous congestion. The European medicinal leech is considered safe and effective for certain medical treatments.
