Leeches: What Do They Do?

What exactly do leeches do? I mean, aside from swimming around murky pools and sticking to people's legs, what do they really do? Well, to answer this question, perhaps it's best if we find out what exactly leeches are first.

What Are Leeches?

Leeches are what we call annelids. They comprise the subclass Hirudinea. There are three types of leeches, fresh water leeches, terrestrial leeches, and marine leeches. Most of them live in fresh water, but there are also those that prefer to live on land, particularly in low foliage or in rain forests. There are also some leeches that can be found in dry forests, but only in places where there is a bit of moisture. During the dry season, these leeches often burrow themselves in the ground, where they hibernate even without water. They simply shrivel up and become rigid and their bodies become very dry. If you sprinkle them with water, they recover completely within ten minutes.

Leeches shown during various treatments

Leeches shown during treatment of
varied conditions

Those that live in the water usually prefer bodies of water that are relatively slow moving and calm. A lot of leeches may also be found in murky waters, which makes them harder to spot.

Leeches, quite interestingly are hermaphrodites - meaning they're both male and female. When they reproduce, one of them merely chooses to play the role of female and another chooses to play the role of male.




They Bite and They Suck Blood

Leeches shown during various treatments

Leeches shown during treatment of
varied conditions


Contrary to popular belief, most leeches don't really rely solely on drinking blood. Some of them actually eat other invertebrates that are smaller than them, swallowing them whole. Some leeches can't bite and are content to feed off decomposing bodies.

Leeches that suck blood are called Haemophagic leeches, "Haemo" meaning blood and "Phago" meaning 'to eat'. They attach themselves to their hosts only until they become full, after which, they will simply fall off and start digesting the blood they sucked out. These leeches suck blood through the anterior sucker which is composed of the first six segments of the invertebrate's thirty four segments. It uses this 'mouth' to attach to the host. They also release some sort of anesthetic, which is the reason why you don't feel the leeches when they bite. They then use suction and mucus to stay on their host. Once they open up a bite wound, they secrete an anti-clotting enzyme called Hirudin into the bloodstream so that blood will keep flowing. Sometimes, blood will continue to seep for hours after the leech has been removed, which is due to the anti-clotting enzyme in their saliva. While this may sound terrifying, being bitten by a leech isn't deadly or dangerous.

Leeches shown during various treatments

Leeches shown during treatment of
varied conditions

They're not really the villains that popular media often portrays them to be. In fact, leeches are actually very harmless. The amount of blood lost due to a leech's bite isn't really significant and when they're full (which doesn't take long), they simply fall off and go on with their lives.

People who bushwalk and don�t want leeches to attach, despite being relatively harmless are known to touch them with a cigarette end or a lighted match to release their grip, or they pour carbonated drinks over the leech. However, doing this can cause the leech to vomit its stomach's contents into the opening wound, thereby increasing the risk of infection. So, it's best if possible to disable their suckers by using a fingernail under the narrower end of the leech and flick them off. Never try to tear them off or it'll worsen the wound, cause the leech to regurgitate its stomach contents, and possibly leave a portion of the leech's mouth on the skin.

They Also Heal

Blood expelled after different treatments

Blood expelled after different treatments


Some of the popular leeches are the European Medical Leech or the Hirudo Medicinalis and some congeners. These are the ones used in the field of Medicine for microsurgery, grafting, and for reconstructive surgery. In the past, these leeches were used to cure infections and for bloodletting. They were quite popular during the medieval ages because they were known to cure infections; in fact, they remained great options for treating infections until antibiotics were discovered.

Doctors use leeches for microsurgery due to their ability of removing blood that has coagulated. They relieve venous congestion and muscle flaps. Leeches are also known to treat black eyes! Hirudin can be used to treat infections of the middle ear and is being tested as a systemic coagulant.

When used for medical purposes, a leech is NEVER used to treat more than one person, as bacteria and viruses present in their former host can transfer to the new host.