What happens when you put salt on a leech?

Michelle Po
23 January 2012

Above: Image © Wikipedia Media Commons

Leeches, those slimy, black blood-sucking organisms, can unnerve even the bravest of lake swimmers. However, you don’t have to panic (too much) if you find a leech has followed you out of the lake after a swim.

Did you know? Leeches release an anesthetic, which is why their bite is usually not felt. Leeches also secrete a chemical that prevents blood clotting. Therefore, wounds may bleed longer than usual after the leech is removed.

A common folk remedy for removing leeches is to pour salt onto the leech. This is a practical example of osmosis, the movement of water from an area of low salt concentration to an area of high salt concentration through a membrane. After adding salt, the salt concentration is now higher outside of the worm, and water moves from the inside of the worm through the skin of the leech. As leeches have a very thin skin, water moves out of the leech very easily, causing the leech to dehydrate and fall off.

Did you know? Leeches are used for medical purposes. They can be used to reduce swelling in injured and transplanted tissues.

However, as effective as it is, this salt treatment is not recommended as a removal method, as it may cause the leech to regurgitate its stomach contents, which may contain bacteria that can infect the wound.

Pulling the leech off is no better, as part of the jaws may be left in the wound. Instead, the safest way to remove a leech is to find the head (the thinner end) and slide something flat, like a fingernail, under the head to break the suction, repeating for the posterior end. If you can stand it, the easiest method may be to let the leech drop off by itself once it has had its fill, after about 20 minutes.

Did you know? In a strange case in Australia, DNA extracted from a blood-filled leech found at a crime scene was used to convict a man of armed robbery.

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Michelle Po

I am currently doing a PhD at the University of Toronto in Molecular Genetics. I'm studying neuronal connectivity using the microscopic nematode Caenhorabditis elegans as a model organism. When I'm not in the lab, I enjoy playing ultimate frisbee, photography, and do-it-yourself crafty projects.

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Avatar  TheMoreYouKnow

"Pulling the leech off is no better, as part of the jaws may be left in the wound." This is wrong. An old myth. It is fine to pull a leech off, but you will just bleed for a while, no mouth parts will be left in the wound. The leech uses an anticoagulant to drain your blood, so it is best to let the leech finish up and fall off naturally, sealing up the wound as it does so. You will lose less blood if you let it finish up and fall off than you will if you pull it off and bleed for a while.


Avatar  Rylen Robertson

Leeches also bite their prey as well as extract blood from them. If it weren't for the bite, the leech would not be able to extract blood. Its biting end breaks open blood vessels, and the vacuum end of it sucks blood out.


Avatar  harriet

I have a question about salty foods


Avatar  Rylen Robertson

What question is that?