Bloodletting with leeches seems a very primitive practice. So, it may surprise you to know it’s still very much in use today.

There are 700 species of leech. Most dwell in water and drink blood from fish, turtles, ducks, frogs and other creatures. Scientists can even track which animals are living in swamps and rainforests by capturing leeches and DNA testing the blood in their stomachs.

Leeches were first used in medicine at least 2,500 years ago. They became so popular in nineteenth-century Europe that overharvesting made them threatened.

Today, we’ve recognized that leeches do in fact have surprising medical benefits.

When they bite to extract blood, they inject over 60 compounds in their saliva that work as blood thinners, anti-inflammatories, antimicrobials and anesthetics. We’ve synthesized several of these and use them widely.

We even still use the leeches themselves. In the U.S., they’re approved as medical devices!

When surgeons reattach extremities like fingers or hands, leeches can be used to slowly drain blood that otherwise might pool and become deoxygenated.

Tests have found that natural anesthesia from leeches is highly effective in controlling pain from joint diseases like rheumatoid arthritis. And they’re used for treating vein disease as well.

So, if you need a medical procedure in the future, don’t be too surprised if your doctor prescribes leeches!