Leeches: fearsome, ferocious, and… friendly?

Today’s blog comes from Charlotte Westcott, Discovery leader at Neys Provincial Park.

One of the most exciting things about working for Ontario Parks is getting to investigate all the different species that live in your area.

Here at Neys, we have a diverse array of boreal forest flyers, runners, critters, and crawlers to investigate.

Yet for all our curiosity about the world around us, sometimes a few of our park residents can slip through the cracks.

Even for some park naturalists, critters can get a bit too… disgusting. Yet if we challenge ourselves to look past the grossness, we can find a whole new world of wonder on the other side!

These fearsome, ferocious, and friendly species have marvelous stories, adaptations, and more just waiting to be discovered once we give them a second look.

Discovering leeches

One day as I was talking about the wonderful world of wetlands to park visitors, an inquisitive kid walked up to me holding a leech and asked what I knew about them.

leech under microscope. Tan with striations, like burlap and black eye spots
A leech under a microscope. Look at those black eyespots towards the front and intricate designs on the outside of this leech!

As I looked at that squirming black ribbon, I realized that in my quest to learn more about wetlands, leeches hadn’t crossed my mind!

At the time, all I knew was they were gross, terrifying bloodsuckers ready to attack the second I stepped into any murky, shallow water.

Yet as I pondered that leech, I wondered how much of that was true.

For being the cause of one of the most dreaded wildlife encounters for many paddlers or swimmers, I had to consider how many times had I actually been bitten by a leech.

How painful was each bite? How much of the stress of the situation had come from my reaction instead of from the leech itself?

With those questions in mind, I set out to explore the wonderful world of fearsome, ferocious, and harmless leeches.

leech on turtle's shell
Spot the leech! That’s a big one!

The information I discovered has totally changed my perspective on these “dreaded” creatures and removed a significant amount of the fear I had about swimming in lakes and rivers!

Fearsome and ferocious?

Leeches are significantly less gross than I thought they were.

My mental image of a leech was an elusive predator lurking in wait for human blood. Yet leeches are not very interested in humans at all.

Humans are a rarity in a leech’s habitat. A difficult prey that only shows up occasionally to intrude and stomp all over their remote muddy homes.

Additionally, of the 35 species we’ve discovered in Ontario, most are uninterested in humans. The ones who do care for our blood are categorized as “medicinal leeches.”

Not exactly the scariest name around!

leech eggs (like two water droplets) on a rock
Two leech eggs or cocoons. Unlike your typical cocoon, sometimes leeches will have multiple babies hanging out in a single cocoon!

Some leech off worms, snails, fish eggs, and aquatic insects. Others scavenge and feed on the remains of dead animals and plants.

More ambitious leeches target fish, frogs, and turtles. Most of them live a quiet life hiding in shallow, stagnant water under rocks, sticks, logs, and decaying leaves.

The way leeches work is quite interesting too!

black finger-length leech on rock
Leech or mysterious abandoned blob of acrylic paint? Definitely leech

Leeches have a main sucker on their mouth (a.k.a., the oral sucker) so they can stay attached, and a sucker on their bum (a.k.a., the posterior sucker) to help them move.

While I usually imagine leeches ribboning through the water, they can often be found inching their way around in a looping motion as they try to find things to latch their mouth or bum on to.

Part of their scariness has always been how “gross” they are. These are bloodsuckers, after all; they’re parasites looking to feed off you!

Mosquitos and ticks are well known for the diseases they carry, yet they don’t have the sheer “yuck factor” that wet and slimy leeches bring to the table.

However, leeches are shockingly polite diners. They don’t carry any known diseases and even clean up after themselves!

Friendly? Really?

Have you ever been bitten by a leech? How long did it take you to notice it was there? How much did it hurt?

muddy black leech in cup
Fun colours! Look at those spots and stripes. We can also see it stretching forward trying to find something to suck on to

I’ve been bitten by quite a few leeches over the years on backcountry canoe trips and ill-fated swimming adventures.

One of the most memorable leech bites I had was when one squirmed its way under my sock and hitched a ride after a portage.

I didn’t notice it was there until around thirty minutes later when I pulled down my sock to scratch an itch and accidentally pet a leech instead! (I might have screamed a little.)

Yet once the initial jump scare was over, I realized it had been tagging along for a ride for quite a while.

With detached curiosity, I realized the bite didn’t hurt at all. It was a faint, itching sensation. By the time we reached the side of the lake and stopped to remove it, my little hitchhiker had already detached and was ready to go on its way.

Medicinal leeches

The most well-known leech in Ontario is the American Medical Leech. Far from a fearful name like the American Bloodsucker or the Vampire Worm, these leeches are labelled for their usefulness.

While we might think that leeches are confined to medieval medicinal practices, they still have a place in modern medicine and are used to draw blood out of reattached body parts and get circulation moving again!

hand holding leech
A blobby, slimy leech fresh from the net and showing off its sucker!

Part of their role in modern medicine has to do with their saliva.

Leech saliva has two main components. The first is an anticoagulant to make blood thinner and flow faster so they can eat more.

The second is a numbing agent — leeches have evolved to make it harder for you to tell they’re biting you! It takes around 45 minutes for them to drink their fill and they don’t want you to flinch in pain and panic to remove them before they’ve finished eating.

That’s how my little hitchhiker was able to stay in the top of my sock for so long.

Although leech bites may be thought to be a painful, scary encounter, the way we deal with these slippery blobs can be even more concerning.

Let them keep their lunch down!

The two most common home remedies for removing leeches are putting salt on them or lighting them on fire.

The reason it makes them let go is for much the same reason we would react if someone threw salt on us or set us on fire. They start to panic.

Except leeches have a very specific reaction to panic… they vomit! So if you use salt or fire to remove a leech, you’re putting yourself at risk of them vomiting their last meal into you.

These “traditional” ways of dealing with leeches are even more unsafe than the leech itself.

There’s a better way

You have two options to remove a leech without the risk of blood vomit:

  1. Wait for them to detach. Depending on when you noticed the leech on you this can take up to 45 minutes.
  2. If you can’t wait, quickly slide a credit card or similar object between the leech and your skin to get it off you before it has a chance to react.

Looking at leeches differently

The lesson I learned from leeches now informs everything else I do in my job.

Every day I wonder what else I’ve been missing in the boreal forest and seek out new topics to share with my coworkers.

If universally hated things like leeches can hold so many wonders and mysteries, what else is out there to discover?