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phylum: Annelida, subclass: Hirudinea


This page is about leeches. While not the most attractive wildlife living in Hotel Lake, it is certainly a species that deserves a closer look, if only to better understand this rather misunderstood creature.

They are part of the phylum Annelida group that includes earthworms and marine sand worms. Approximately 700 species are known to exist and they inhabit every continent aside from Antarctica. Canada hosts about 60-70 species.


Many freshwater leeches are carnivores but they stick to molluscs, insect larvae and worms and don’t eat blood at all. The ones we see attached to our skin are popularly labeled “blood-eaters” but even these aren’t actively looking for human blood because they prefer naturally occurring small aquatic creatures and plantlife. On the other hand, if a human is swimming nearby, these leeches are perfectly situated and inclined to take advantage.

We titled this page, “phylum: Annelida, subclass: Hirudinea”;  phylum Annelida means “leech”,  subclass Hirudinea includes about 650 species of leech which have 34 body segments, a small sucker, which contains the mouth near the head and a large sucker located at the posterior end. The subclass Hirudinea are leeches that produce, in their salivary glands, a peptide with anticoagulant properties, called “Hirudin”.


With up to 70 species in Canada, it is difficult for us to say precisely which order, family, genus, or species might be in our lake.  But we have found a number of references that discuss leeches of the “blood eating” variety which appear very similar to those leeches many of us have seen attached to our skin after a swim. We believe our local leeches are most likely of the “Hirudinea” subclass.

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Let’s begin with the leeches that we sometimes see on our skin after swimming in Hotel Lake.  They are usually quite small and black or grey-green in colour. They have front and rear suckers which allow them to walk like an inchworm on the lake bottom. The leech’s front sucker is also its mouth, or jaw.  


They are described in literature as hardy and long-lived and can be found in all BC Coastal Region lakes, ponds, rivers, streams, bogs, and swamps. Muddy bottomed nutrient-rich waters are often home to prolific leech populations. 

Generally speaking, leeches are opportunistic feeders and will consume a wide variety of aquatic food types such as small snails insects, larvae, etc. and some also consume blood from animals and humans if the opportunity arises to do so.

Humans swimming in Hotel Lake may encounter leeches but in most cases they go unnoticed. This is because they have evolved with the ability to produce both anticoagulants and anesthetics in their saliva which they inject into their prey as they bite.  This is a remarkable combination indeed, the anesthetic makes sure that the animal or human does not feel anything while the anticoagulant ensures the blood flows freely into the mouth of the leech.

At this juncture, it is important to emphasize that a leech, when it bites to draw blood, does not transmit disease.  Mosquitoes and ticks are famously known to carry and deliver diseases to humans but leeches do not.

Later we will present information about what to do if you find a leech or two on your person after swimming.


Life Cycle and Reproduction

Leeches are believed to live for 2-8 years. Locally, they can grow to a modest size between 3 and 7cm in length. Colouration is usually  black, with camouflage variations that may include brown and green and even reddish accentuations.


They are an important component of the bethnic (lake bottom) community and can be found living near the bottom of Hotel Lake in shallow water less than 8 metres deep, either on the substrate or inside it, buried or burrowing in the sediment.  This is because their preferred food sources are found amongst the vegetation, rocks and deadfall associated with shallow areas of the lake that receive the greatest amount of sunlight. Parasitic leeches feed on a variety of vertebrate, like fish, turtles, frogs and mammals, including humans. 


A leech is an annelid and its internal structure is divided into 32 separate segments (some sources say 34). The leech’s brain extends through these segments but because each segment operates independently, it can be said that a leech, physiologically, has 32 brains.


They are excellent swimmers. If they need to swim rapidly they employ a remarkable capability to change shape quickly. By flattening and elongating their bodies they achieve an efficient streamlined shape that allows them to “swim” by moving their body in an undulating wiggle.  If they need to move more quickly or urgently in pursuit or escape, they can accelerate as the need arises. When viewed swimming underwater, they can be mistaken for a small snake.

They have simple eyes, located towards the front of the head, which detect variations in ambient or reflected light. It is believed that their visual capability may include a perception of movement, however they lack the visual acuity of most aquatics or amphibians. Their situation awareness is bolstered by sensitivity to chemoreception which provides a sense of taste/smell and mechanoreception, the ability to detect and react to touch. The scientific community continues to research these areas for better understandings of how leeches react to surrounding stimuli. They are nocturnal creatures. During daylight we know that they are attracted to water disturbances made by animals or people swimming or wading nearby.

Leeches are hermaphrodites that possess both male and female sex organs, however, they cannot self-fertilize. Mating is accomplished when leeches intertwine their bodies and, in so doing, fertilization takes place. New born leech eggs are protected by a gelatinous cocoon which may be attached to any available surface or simply buried in the lake bottom.  After a few weeks the infant leeches emerge. During this period some species of leech watch over the eggs until they are born.  Leeches are believed to die after one or two cycles of reproduction.

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The Medicinal Leech

Records of leeches being used in medicine go back some 2500 years. These early leech treatments were applied for much the same reasons as was the practice of blood letting. The use of leeches in Europe peaked between 1830 and 1850 but then declined. Leeches are used today for a number of sophisticated medical purposes including treatments for arthritis, blood-clotting disorders, varicose veins, and other circulatory disorders, as well as in plastic and reconstructive surgery. For surgeons, leeches have become useful modern tools to support blood flow during recovery from surgical reattachments of amputated parts of the body. 

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Leech as Bait

Leeches are an  important  component  of the  benthos (bottom environment)  of most  freshwater  lakes,  ponds,  and quieter flowing sections  of  streams and  rivers. In these environments they are also part of the food chain.  Leeches make perfect food for larger fish such as the cutthroat trout in Hotel Lake.  If trout love leeches then so do anglers who utilize live leech bait or a wide range of artificial tied lures, made of rabbit fur, etc. Hopefully, such lures on the hook of a skilled fisherman, will mimic the appearance and movements of an actual leech making it irresistible to trout.

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A Leech Can Bite

When a leech bites a human it usually creates tiny interconnected incisions.  In certain leeches it is a V shape and in other leeches a Y shape.  You won’t see this until after the leech drops off.  You also won’t feel anything because the leech has secreted an anesthetic to stop pain.  The anticoagulant, hirudin, is also secreted so you can expect some degree of bleeding following the removal of the leech.

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About Leech Bites

First keep in mind that a leech, while attached to you, is almost certainly not transmitting any disease into you and most leech bites are harmless and do not require medical attention. 


In rare cases, some people may experience an allergic reaction to leech bites and people with a history of allergies or anaphylaxis need to be extra careful.


Those who are taking anticoagulant medications are at risk for more prolonged bleeding after a bite.


In addition, most leeches carry the bacteria Aeromonas in their gut, which could infect the leech site. A person who has been exposed to a leech might take prophylactic antibiotics as a precaution.

It should also be noted that research indicates that rare cases of the transmission of bacterial disease like Hepatitis B or Malaria can occur. Also, some leeches have been found to host HIV however there is no evidence of transmission to humans. 


What to do if bitten?

There are many sources with information on what to do if bitten along with how-to-remove a leech suggestions.  We have collected this information and present it below:

Because a leech may harbour various bacteria in its gut or elsewhere in its body, great care should be taken not to squeeze the leech or introduce blunt force trauma by hitting it, both of which might force digestive tract contents into the bite area. 


Avoid using salt or trying to burning the leech or any other dramatic option as such severe and painful actions may cause the leech to regurgitate blood back into your body which may cause infection.


If you are not in a rush, the most natural way to get rid of the leech is to simply wait until it finishes feeding (30-45 minutes) after which it will drop off.


If you decide to mechanically remove it, try using a credit card or finger nail to pry under the leeches sucker(s)  and gently lift it off your skin.


Returning the leech quickly to the lake water is a kindness.​

We attach, without edit, the following expanded steps as published by Healthline


The basic leech removal steps are:


Locate the head and mouth. A leech’s head is smaller and slimmer than the rest of its body. Look for the narrowest part of the leech to locate its mouth. This is usually the part attached to your skin.


Pull the skin under the leech taut. Use one hand to gently pull your skin under the leech until it is taut.


Slide a fingernail underneath the mouth. Gently slide a fingernail under the leech’s mouth to separate it from your skin.


Flick the leech away. Use your fingers to flick the leech away before it reattaches.


Clean the wound. Clean your wound with rubbing alcohol or a first-aid cleanser to help avoid infection.


Bandage your wound. You’ll see a lot of bleeding when you remove the leech. Clean the wound and then use a sterile bandage to cover it. Change the bandage frequently for the first few hours until bleeding stops.


Healthline, “the fastest growing health information site. Over 200 million people turn to Healthline every month.”  We include the following direct link to “Healthline” because it has much more to offer for those interested.


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