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Blood-sucking parasite or unappreciated lifesaver?

• John Lorson: The Rail Trail Naturalist
• April 23, 2021
• 2080

You never know what you’ll find while strolling along on a sunny day in late April. Last week I was out doing some research along Killbuck Creek with a colleague when I spotted a wriggle in the mud of a two-track lane. I had remarked only moments before that this was a “snaky” kind of day, and we were definitely surrounded by some impressive snake habitat on all sides. When it’s cool in the shadows but warm in the springtime sun, the reptiles in our midst tend to work their way toward well-lit spots to warm themselves.

A prime example of this basking behavior can be found on darn near every stream bank, mudflat or floating log in the Killbuck Valley at this time of year as turtles clamor for their spot in the sun. Be assured there are plenty of snakes doing the same sort of thing right now, but as solitary beings (except for some overwintering situations), snakes tend to spread out and are infinitely more stealthy than the rightfully fearless turtle whose aerial predators are few. A snake on a log appears as a sausage in a skillet to a bird of prey.

Back to the story at hand and that “wriggle in the mud.” At a glance my first thought was it was a tiny black rat snake, and at 6 or 7 inches, it would be the smallest I’d ever found. As I moved closer, however, my “snake” actually shrank to half of its length. That’s when I realized I was looking not only at a different species, but a different organism altogether. This was no snake, nor even a reptile for that matter. The creature in the mud hole was a leech.

Anyone who’s ever caught a turtle from a pond or poked around in the swamp for frogs has likely encountered a leech — small, black and creepily squirmy. They’ve probably saved a whole lot of marshland critters from being carried home to the family aquarium.

This particular leech picked the wrong mud hole on the right day (for me at least) because I knew in a heartbeat I needed to catch this guy, take a closer look and learn a little something. (Actually “guy/girl” would be more appropriate because, just like their close cousin, the earthworm, leeches are hermaphroditic and are both male and female at the same time.)

The American terrestrial leech, or “mud leech,” I found is one of 79 species of leech that call North America home. As a limicolous or “living in mud” member of the leech family, it is one of only 15% of leech species worldwide that do not live entirely in the water. Most leeches dwell in freshwater habitats. And yes, salt does kill freshwater leeches (by altering fluid balance); however, 15% of species are actually adapted to saltwater environments. You’d need a different weapon to terrorize those critters, but why mess with them anyhow?

Leeches are for the most part harmless to humans and most other creatures. For many species, “sucking blood” is only one option for feeding. My mud leech buddy for instance prefers to eat earthworms, and swallows them down whole.

Much of the time when you find a leech attached by its tail to the carapace of a turtle, it’s simply along for the ride. My “research subject” was pretty quick to grab hold of my finger with the “suction cup” at its tail end. And it left a mark when I pulled him off, but nothing more than a tiny bruise — not a bite. Had the creature been interested in sucking my blood, it would have attached with its mouth at the other end and injected a small amount of saliva, which contains all sorts of compounds from anticoagulants (to thin and keep the blood flowing) to vasodilators (to enlarge tiny blood vessels).

As “blood sucking parasites” go, the bite of a leech is typically of little or no consequence to its host. It’s a whole different ballgame than the bite of a tick or mosquito. As a matter of fact, leeches have been used for at least 2,500 years in medical applications and are still used today, particularly in situations of reconstructive surgery where blood may pool in tissue. Those compounds in the saliva can keep the blood flowing and prevent tissue damage. And as an added bonus, a built-in anesthetic makes their work pain free.

While my leech was the type of fellow/gal that would likely be found in a bait box rather than an operating room, it still offered an interesting opportunity to take a closer look at a creature that deserves a little more respect than one might imagine. After a brief tour of the office, during which I did my best to gross everyone out, I set him free on a muddy stream bank along my bicycle route home. No leeches were harmed in the writing of this column.

Remember, if you have comments on this column or questions about the natural world, write The Rail Trail Naturalist, P.O. Box 170, Fredericksburg, OH 44627, or email jlorson@alonovus.com.