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Why do leeches suck our blood? – Thomas, 6 years old.
The short answer is that leeches need blood to grow and reproduce (make leeches).
Leeches are worms that live in water or on land and feed by sucking blood from fish, frogs, lizards, birds or, if they have chance, larger animals like humans.
They suck blood because it is a very good food for them. Some leeches need only feed once a year.
The only problem with sucking blood is that you have to do it very carefully, especially if the animal from which you are sucking is able to bite it or pull it out. So leeches, like all bloodsuckers, usually like to bite without causing too much pain. They like to bite in places where they are hard to find.
Blood clots, but leeches have a solution
The other thing that leeches have to worry about is blood clots. A blood clot forms whenever you receive a cut that stops the bleeding in a few minutes – eventually the blood clot forms a crust.
This happens when the blood comes in contact with the air. It clumps and forms a solid core. The leech can not feed itself if the blood forms a lump and therefore releases a chemical substance that avoids that lump.
This keeps the blood flowing so the leech can suck for two or three hours without stopping. That way, he collects enough food to last until he finds another animal to bite.
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Leeches are not the only animal that feeds on animal blood. Others include mosquitoes, ticks, vampire bats (yes, they exist, but only in South America), bedbugs, lice, other insects and the lamprey. All these feed on larger animals – but do not kill them, so they are all called parasites.
All parasites live on or in other animals and many of them feed on blood. Blood is easy to collect if you are in or out of the body. It is highly nutritious and there is always plenty, so the animal that the parasite is feeding can usually save a little.
Leeches and Remedies
Leeches can be irritating and their bites can leave us with itching but are generally not dangerous to humans. In fact, leeches have been used to treat human diseases for thousands of years. It was believed that their ability to suck blood was useful for sucking sick or "bad" blood out of the body and sick people had leeches regularly.
However, we now know that allowing leeches to suck the blood does little to help in most cases. In fact, if many leeches are applied, a sick person may become weak from the loss of blood.
The only area of medicine where leeches are still useful is to use them to improve blood circulation in the skin. They also reduce the chances of blood clotting when this can be dangerous in some sick people. However, nowadays we can make an artificial version of chemical leeches to prevent blood clots, which is called "hirudin".
Leeches need blood to grow and reproduce, which they can easily do, since all leeches are male and female at the same time. They still have to mate with another leech, but both partners can lay eggs after mating.
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