American Medical Leech

Photo by: K. Leeker

Many years ago, when working for the Missouri Department of Conservation, I was helping a local professor locate frog eggs in an ephemeral pond. This particular pond was located within the woodlands behind the building where I worked. After finding some eggs and wading into the water to collect them I became all to aware of what else was living in that small pond. LEECHES! I exited the water and to my surprise I found two leeches attached to my legs. I didn’t know whether to be fascinated or grossed out. Then I remembered something I was once told, “A dedicated nature enthusiasts never says “EWWW”, instead they exclaim “OHHHH, how interesting.” I did my best in that moment to be a dedicated naturalist, who other naturalists could be proud of, but the ick factor got the better of me and I quickly evicted these little bloodsucking vampires from my person. After all these years I have never forgotten that moment, which goes to show what a lasting impression these parasites can leave on our psyche.

There are nearly seven hundred species of leeches found worldwide. Leeches are found in freshwater ecosystems, a few are found in marine habitats, and rarer still are species that are terrestrial and live their lives on land. Slow-moving freshwater habitats such as streams, lakes, and ponds are the preferred habitat for most species, and under the best of conditions may have as many as 7,000 individuals per square meter! The lions share of leeches are sanguivorous, meaning they feed as blood sucking parasites. A small portion of leeches are predators and feed on small invertebrates and snails, some may even feed on other leeches, even their own kind. Leeches are part of the same group of animals as earthworms, and just like their worm cousins are heavily muscled with flexible segmented bodies. They range in size from less than an inch to nearly twenty inches and may grow as much as five times their normal body size after feeding. They are VERY stretchy! Many species have suckers located at each end of their bodies; these suckers allow them to move much like an inchworm moves. You may find them inching along under the surface film of the water hanging onto the sticky top layer of water molecules with both rear and front suckers. They are undulating and graceful swimmers preferring slow-moving, warm watery habitats. They will also move in this inchworm-like way on the bottom of ponds or other watery environments they are found.  Ephemeral ponds frequently dry up during extremely hot weather or during seasonal droughts. When this happens, the leeches will burrow into the mud, waiting for rainy weather and optimal conditions to return. They may survive a year or more without a blood meal!

For more than 3,500 years, leeches have been used for medicinal purposes. As far back as Pliny the Elder leeches were used as a means for bloodletting. Early physicians called leeches, a word derived from the old English word “leace” and translates to mean doctor or physician. These early physicians believed the body was made up of four “humours” that included blood, phlegm, black bile, and yellow bile, By applying leeches to slowly remove tainted blood from their patient, doctors of ancient times used them to cure patients of many medical complaints that ranged from gout to sore throats. It has long been believed that George Washington died from overzealous bloodletting by the presidential physician. Complaining of a chronic sore throat, Washington was bled four times in two days, relieving our first president of valuable blood supply and ultimately claiming his life.

Napolean Bonaparte imported six million leeches to treat his soldiers of various ailments. Most likely to help treat amputations and necrotic wounds. It has long been known that leeches can improve blood circulations which greatly increases the chance you will recover from a serious wound with no serious infections.

By the mid-1800s demand for leeches was so great that the French imported four million leeches a year for medical purposes. Eventually England jumped on the leech bandwagon and began importing as many as six million leeches a year from France. This was a lucrative field of work; in which individuals would collect leeches from any and all available water sources. This over collection greatly reduced their populations. Today medicinal leeches are bred and raised in sterile conditions that is referred to as hirudiculture. No fear of wild caught leeches being used to treat what ails you. Today leeches are used to help heal wounds after reattachment surgery, to help with healing tissue after plastic surgeries, as well arthritis and circulatory related health issues which is but a few beneficial aspects of their natural feeding habits.

Because leeches are more frequently parasitic than predatory by nature, the host, or prey they feed on get to live another day. Typically, they will feed on the blood of frogs, and other amphibians. Some individuals say if you want to remove the leeches from your pond, remove the frogs. I personally would not be a proponent of that strategy, as removing frogs from an established habitat creates another set of problems that can and does greatly affect the food chain in your pond. Some leeches are specialist though and feed only on fish, or perhaps turtles, others are generalists and don’t seem to care where their next blood meal is coming from. Using chemical receptors on their head provides a sense of smell and those that possess primitive eyes called ocelli can detect chemicals, light, heat, pressure, touch, and disturbances in the water. I am sure it was these opportunistic bloodsuckers that set their sights on my legs that day. My wading in the shoreline would most definitely be a disturbance in the water no respectable leech is going to pass up.

Most leeches release an anticoagulant and a form of painkiller to attach themselves without notice and allow for blood to flow freely for easier feeding. It may take a few minutes or up to an hour or more for the leech to feel satiated and release their host. If you find yourself in a predicament like I did, gently remove the leech using your fingernail to release the suction of the leeches mouth. Pulling on it may leave mouth parts behind causing severe itching. Do not use chemicals to remove the leech, while vinegar, turpentine, and alcohol will make it let go, it will also cause the leech to vomit in the wound potentially creating the perfect conditions for an infection to establish itself. Generally, bites are not painful (although there are exceptions), and do  not cause any lasting effects, but on the rare occasion that a person finds themselves allergic to the enzymes in the leeches saliva, a bite can be serious enough to require medical attention. Serious reactions would include red blotches, an itchy rash, swelling around the lips or eyes, feeling dizzy or faint and difficulty breathing indicating an anaphylactic reaction. In even rarer cases bacteria, viruses, and protozoan parasites from previous blood sources can survive within the leech for months and may potentially act as a vector and pass those pathogens onto the next host. However, this has only been confirmed on a few occasions.

If you are not completely grossed out and disturbed by the very idea of leeches, you can keep them as a pet that is sure to render some interesting conversations by visiting guests. Just feed them some snails or raw hamburger and your pet may stay around for more than ten years. Like many animals living in nature, they possess benefits to humans or other living creatures. In the case of the leech, it has helped in many medicinal ways for more than three thousand years, they provide food for fish, as well as a variety of other predators, including other leeches. If you find yourself the unexpected host of a bloodsucking leech…. remain calm and like all dedicated nature lovers say to yourself “how interesting,” then you have permission to freak out.