Leeches can remain attached to their prey for a long time thanks to their powerful suction cup which creates a strong suction, and their saliva containing anticoagulant substances that limit bleeding and facilitate their meal.
Leeches have two special ends called suckers, one at the front and a larger one at the back, allowing them to hold on tightly. The front sucker conceals a jaw with tiny, very sharp teeth, often arranged in a Y shape, capable of easily piercing the skin. Their soft, flat, and muscular body not only allows them to flatten against their victim without drawing attention but also to easily contort when the victim moves. Additionally, their skin is covered with a thin, slimy layer that enhances adhesion and facilitates movement on the prey, without the prey really noticing.
Leeches have two muscular suckers, one at each end of their body, but it is mainly the frontal sucker, surrounding their mouth, that allows them to firmly attach to the skin of their victim. This sucker consists of powerful circular muscles capable of creating a sort of partial vacuum, like a small silicone suction cup pressed against a smooth surface. By contracting, these muscles progressively expel the air and water present, securely adhering the leech to the skin. Once attached, it can forcefully suck blood using its muscular pharynx, which acts as a pump, effortlessly maintaining its connection with its prey despite all movements or attempts to detach.
When a leech bites, it doesn't just suck blood: its saliva contains special substances called anticoagulants. These molecules prevent the blood from coagulating (from forming clots), allowing the leech to continue feeding calmly for an extended period without the wound closing. The most well-known of these substances is hirudin, which is reputed to be very effective at thinning the blood. Thanks to it, leeches have all the time they need to have their meal without having to constantly reopen wounds, which would be tiring and risky for them. These anticoagulants can have lasting effects on the host even after the leech has let go, sometimes causing prolonged bleeding.
Leeches have skin that is both flexible and permeable, perfectly adapted to aquatic environments, allowing them to exchange oxygen directly with water through simple diffusion. There is really no need for evolved lungs in their case. Moreover, their flattened and elongated body significantly reduces water resistance, discreetly facilitating their approach to prey without being detected. They also effectively manage their internal balance of salt and water, allowing them to remain attached for long periods without being disturbed by changes in their aquatic environment.
Leeches use an effective combination of dark colors and flattened shapes that allows them to remain virtually unnoticed while clinging to their prey. Their appearance often beautifully mimics dead leaves, twigs, and even stones at the bottom of the water. Discreet, they attract no attention; even their initial bite is often painless due to anesthetic substances secreted by their salivary glands. Some species change slightly in color depending on their environment, thus enhancing their natural camouflage and allowing them a lasting peace during their meal.
Leeches have not only an oral sucker to bite their prey, but also a second sucker located at the rear end of their body, ensuring optimal attachment while remaining sufficiently mobile.
Some species of leeches have an impressive ability to perceive movements and vibrations in the water. They can detect their prey from several meters away simply through vibrational signals.
A leech can ingest an amount of blood equivalent to five times its own body weight in a single feeding and can survive for months without eating.
The anticoagulants found in leech saliva are so effective that they are used in modern medicine to prevent blood clot formation after certain surgical procedures.
A leech can remain attached to its prey for 20 minutes to several hours, or even several days depending on the species, until it has absorbed a sufficient amount of blood (up to 5 to 10 times its own weight). Afterwards, it detaches spontaneously.
No, the bite of a leech is generally harmless. However, their saliva reduces blood clotting, which can cause slight bleeding once they detach. It is recommended to thoroughly disinfect the wound after removal to prevent any infection.
To safely remove a leech, it is best to wait for it to detach on its own. If you want to remove it immediately, gently slide your nail or a thin card under its anterior end to break the suction. Never use violent methods (such as a cigarette, salt, or alcohol) as they can cause the leech to regurgitate bacteria into the wound.
Although relatively rare, there is a slight risk that leeches can transmit certain infections or bacteria when they bite. This mainly occurs if they release bacteria present in their digestive tract due to improper handling. It is advisable to thoroughly clean the wound after the leech detaches.
Some species of leeches are used in medicine due to the powerful anticoagulant and anti-inflammatory properties of their saliva. For example, they help improve blood circulation in cases of grafts or organ reimplantations and contribute to preventing the formation of blood clots.
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