Facts about Leeches

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.

Most are aquatic or amphibiotic (adapted to live both in water and on land); species that live on land are rare.

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.

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.

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.

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.

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.

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.

Many leech species take care of their offspring by carrying the young on the abdominal side of the body for some time.

They absorb oxygen with their entire body surface.

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.

It is a treatment method known to humanity since the beginning of civilization.

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).

In June 2004, the US Food and Drug Administration approved leeches for medical use, recognizing them as a therapeutic agent.

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.

Approximately 0.015 g of hirudin can be obtained from one individual.

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 

These include other leeches, crayfish, some species of aquatic insects and their larvae, fish, waterfowl, and some species of mammals.

By parasitizing fish, they cause significant damage to fish farming.