The Leech Craze: The Medical Fad That Nearly Eradicated A Species

In October 2018, a man named Ippolit Bodounov boarded a plane from Russia to Toronto, Canada. Although we do not know how he felt as he made his way through the terminal and eventually took his seat for the long intercontinental flight, we can easily imagine he was at least a little nervous. That’s because his hand luggage was filled with something illicit. 

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Still, Bodounov made it through the flight with no issues, but just as he was making his way through Toronto Pearson airport, his bag caught the attention of a dog working with a border agent. The jig was up. His luggage was searched, and what was inside likely shocked the agents. It was filled with nearly 5,000 wriggling, living leeches. 

This may strike you as a weird thing to find smuggled into a country, but it isn’t the only time it has happened. Nearly three years later, in early 2021, a Turkish national was caught trying to smuggle around 4,000 leeches out of the country in a suitcase. After an investigation, it appeared the man did not have a permit to legally transport the parasitic worms, so he was fined for unlawfully attempting to import a regulated species (the leeches were apparently set free). 

So, what’s going on here? Why are people going to such great efforts to smuggle leeches across borders, and why are they listed as a regulated species? The answer has surprisingly deep roots in the excesses of a 19th century fad and powerfully demonstrates just how long-lasting the impacts of some cultural quirks can be. 

Balancing the body

These apparently much sought-after leeches were not just any kind of blood-sucking worm – they were medicinal leeches (Hirudo verbana). These leeches have been used by physicians and other healers from across various cultures for thousands of years. 

The first known use of leeches for medical treatment is recorded in the Ebers Papyrus, an Ancient Egyptian medical text that dates back to around c. 1550 BCE. The idea was later used in India and then by the ancient Greeks and Romans as part of the humoral model of medicine, which remained the dominant medical theory through the medieval period after these ideas were modified and passed on by Islamic scholars.

Today we may feel a bit squeamish about having our blood sucked by a leech, but it fitted perfectly within this extremely influential medical tradition. According to humoral medicine, a body’s health was based on the equilibrium of specific fluids within it: blood, yellow bile, black bile, and phlegm. An excess of any of these fluids, so practitioners believed, would manifest as a sickness in their patients, so a physician would attempt to figure out which humor was too abundant and then try to remove it from the body. 

For instance, if you were thought to have too much yellow or black bile in your body, a physician could prescribe you emetics or purgatives to either make you sick or have a bowel movement. This would bring you closer to balance. Alternatively, if they believed you were suffering from an excess of blood, they would bleed you. This could involve the physician opening a vein with a lancet and letting you bleed into a bowl for a certain period of time (bloodletting), or they may have turned to a handy wriggling friend to do the work for them: your humble medicinal leech.

When a leech feeds on a host, it is capable of ingesting around 5 to 10 milliliters of blood, which is around 10 times more than its own body weight. This may or may not strike you as a lot, but consider that doctors rarely treated a patient with one leech at a time. These little squirmers have traditionally been well fed by the medical community. However, the story took a bizarre and tragic turn (for the leech) in the 19th century. 

Although leeches were a familiar feature of the medical landscape, their true fame took after François-Joseph-Victor Broussais, the Parisian physician, identified them as effectively a cure-all. 

According to the influential doctor, all “fevers” – a catch-all term covering everything from a common seasonal flu to more serious illnesses like influenza, typhus, typhoid fever, yellow fever, malaria, and even smallpox – were caused by inflammation of the organs, which could be eliminated by removing blood from the surrounding area. As leech bites are inflicted using three jaws and also release an anti-coagulant, called hirudin, a person can continue to bleed from the bite for several hours after the leech has had its fill.  

Compared to cutting a person through bloodletting, a leech’s bite was considered gentle and easy to control (you put a leech on a glass jar above the area you want it to feed and then let it do its sucky business). So, this made Broussais’ treatment safe, easy to manage, and extremely replicable. And, during the late 18th and early 19th centuries, Parisian medicine was generally regarded as the most cutting edge and sophisticated medicine of the age, which meant it carried significant cultural weight; soon everyone who was anyone in Europe wanted to have all their ills treated by these hungry worms. 

What followed is pretty shocking: the demand for leeches skyrocketed. For instance, in 1815, St Thomas’ Hospital in London used 1,607 leeches in their treatments. By 1822, that number had shot up to 50,000 leeches. 

In 1833, France imported 42 million leeches into the country for medical purposes and Broussais’ own hospital used over 2 million leeches in the years between 1830 to 1836. In some cases, hospitals had special leech holding pools created so their squirming assistants had a place to live between meals, while the craze led some people to buy their own leeches for personal use at home. 

The enthusiasm for leeches was not universal, however. There where those who saw the craze in a more sinister light, such as Friedrich Alexander Simon, a German physician, who accused Broussaists and colleagues of releasing “vampirism” across Europe. And with any popular treatment, there were those who took it too far. Simon’s misgivings over the widespread use of leeches stemmed from the case of one patient who died after having 1,800 leeches applied to their body.

Population decline

Of course, when the demand for something begins to rise, there is always more pressure on the supply chain. In this instance, the pressures fell on rural workers who had to collect the leeches through some pretty unpleasant methods. In essence, people would wade out into ponds, streams, marshes or other still bodies of water and wait for the resident leeches to attach to their legs for a snack. They’d then peel them off and store them in some sort of bucket or other receptacle. 

It was a pitiable existence. The job was arduous, demanding, and unsanitary. Leech collectors would have to suffer numerous bites, loss of blood, and the risk of waterborne infections. There was also the risk that they could contract other diseases from the previous hosts a leech fed on. 

But as time went by, the leeches’ numbers started to dwindle. This was partially due to the demands of the leech craze, but also the wider cultivation of agricultural land and the draining of wetland ecosystems. The French medical community was so shocked by the loss that it even established a prize of 2,500 francs for the person who could demonstrate a way to repopulate the marshlands and native stocks of leeches.

Although some individuals found ways to farm leeches in France, many other countries were forced to import their stock from the Ottoman Empire, Russia, North Africa, and the Balkans. At the same time, the discovery of what would become known as the germ theory of disease started to challenge the assumptions that underpinned the leech therapies. 

Louis Pasteur’s demonstrations of the specific microorganisms that caused diseases like silkworm disease, chicken cholera, and anthrax helped show that disease was not caused by unbalanced internal systems, but rather by external agents. As the ideas gradually spread, fewer doctors could champion leeches as they once had and medical reformers were increasingly regarding them as outdated, barbaric, unscientific, and potentially harmful treatments (though it should be noted that American opinion on this was more diverse, and some physicians and even barbers continued using native leeches into the next century). 

But the damage was done. By the end of the century, the leech population across Europe had plummeted to near extinction and, later in the 20th century, the parasites were granted conservation status in parts of Europe. 

But while the 19th century leech craze may well demonstrate the costs some of our medical or health fads can have, the story of medicinal leeches doesn’t stop there. For the past 50 or so years, leeches have found their way back into the medical community’s good graces. Increasingly, the slime-glorious critters have become an important and approved aspect of reconstructive and plastic surgery, where they help drain blood that has pooled in a wound while also encouraging blood flow to damaged tissues. It seems the history of our two species will remain entangled for some time to come.