Facts about Leeches

We found 20 facts about Leeches

Animals with unusual properties

Leeches, being eurytopic animals, are common on almost every continent. Although they usually lead a parasitic or predatory life, they have been used by humans for centuries for medicinal purposes. In the past, they were used for bloodletting, today, kept in sterile cultures, they support various medical therapies.

Leeches (Hirudinea) belong to the phylum Annelida.
Annelida includes more than 500 species, which are equipped with one or two suckers. Most of them are erybionts, organisms that show excellent tolerance to environmental factors. They can live in a wide variety of conditions and colonize large areas of the earth. In addition to leeches, eurytopic species include the house sparrow, the common reed, and the common bracken.
Leeches have a parasitic or predatory lifestyle.
Most are aquatic or amphibiotic (adapted to live both in water and on land); species that live on land are rare.
Leeches are found in inland freshwaters as well as in marine waters on all continents except Antarctica.
They can live in freshwater, brackish water, saltwater, and on land. Leeches prefer shallow, still, or slow-moving water. They are not found in rushing mountain streams or raised bogs. Those adapted to life on land (few) inhabit the litter of tropical forests, such as the Ceylon leech.
The body of leeches is elongated, obovate, or dorsoventrally flattened and may range in length from a few millimeters to over 30 cm.
Their bodies are contractile and distinctly segmented, tapering towards the ends ending in one or two suckers. The suction cups are used by the leeches to attach to the substrate, and by the bloodsucking species only to penetrate under the skin of their prey - for sucking they use their strongly muscled pharynx and esophagus. The anterior sucker contains the mouth opening.
The cephalic segment of the leech is made up of a prostomium and four segments.
Eyes are located on the prostomium. There may be from one to ten pairs of different shapes and sizes. Eye positioning varies between species, and there are even ones that do not have eyes at all.
The body color of leeches is shades of brown and green with a hint of black.
In water, leeches move in a wavy, meandering motion.
They move in a similar way to the caterpillars, with the help of suction cups - they extend their bodies forward, attach themselves to the bottom with the front suction cup, and move by contracting the rest of their body.
The vast majority of leech species are parasites, the rest being predatory species.
Parasitic species, which are permanent external (rarely internal) parasites, feed on the blood of vertebrates or the body fluids of invertebrates. Predatory species prey on invertebrates, fry, and tadpoles.
Leeches are hermaphrodites.
They use cross-fertilization and developed complex mechanisms to prevent self-fertilization. Leeches lay their eggs in a cocoon (the number of eggs ranges from 1 to 300) attached to plants, stones, in the soil, or on the underside of the parent organism. Simple development (no metamorphosis) takes place in the cocoon.
The young hatch fully formed and adapted to independent life.
Many leech species take care of their offspring by carrying the young on the abdominal side of the body for some time.
Leeches do not have a respiratory system.
They absorb oxygen with their entire body surface.
Leech saliva has specific properties.
It contains hirudin, a substance that prevents blood from clotting, and histamine, which causes dilation of the blood vessels. The secretion of hirudin causes the blood absorbed into the digestive tract not to clot. This allows some parasitic leeches to feed "in reserve," so to speak - a medical leech, for example, only needs to attack its host twice a year.
Thanks to these properties of the saliva, leeches, especially the medicinal leech (Hirudo medicinalis), are used in hirudotherapy.
It is a treatment method known to humanity since the beginning of civilization.
The first cases of hirudotherapy were recorded in Ancient Egypt.
They are known from wall paintings dating back to the 18th Dynasty (1550-1292 BC). The medical use of leeches is reported in the earliest written sources by Nikander (2nd century BC) and from 1st century Chinese sources, Sanskrit, Persian and Arabic literature. The Romans gave leeches the name hirudo (which Linnaeus adopted for their description).
Pliny the Elder wrote that leeches suck blood and are helpful for "rheumatic pains and all kinds of ailments and fevers."
In June 2004, the US Food and Drug Administration approved leeches for medical use, recognizing them as a therapeutic agent.
More than a dozen species of leeches, primarily from the family Hirudinidae, are used for hirudotherapy.
The most commonly used species are Hirudo verbana - the Asian-Southern European, Hirudo trctina - the African species, Hirudo orientalis - the Asian species and Hirudo medicinalis - the medicinal leech, which is under strict species protection in many countries.
Individuals grown under sterile culture conditions are used for the treatment.
Approximately 0.015 g of hirudin can be obtained from one individual.
Hirudotherapy effectively treats or supports the treatment of many diseases.
These include:
  • diseases of the cardiovascular system
  • thromboembolic diseases
  • atherosclerosis
  • arterial hypertension
  • surgery and replantation
  • diseases of the nervous system
  • inflammatory processes
  • pain therapy
  • diseases of the genitourinary system
  • bacterial infections
  • dermatological diseases and cosmetology 
Leeches provide food for many aquatic and terrestrial animal species.
These include other leeches, crayfish, some species of aquatic insects and their larvae, fish, waterfowl, and some species of mammals.
Blood-sucking leech species carry pathogenic viruses and blood parasites.
By parasitizing fish, they cause significant damage to fish farming.
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