Bug Blog #2: Leeches: The Modern Doctor

Date: May 13, 2017 Author: EcoSpark Categories: Latest
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Welcome back to our second edition of Bug Blogs, celebrating Science Odyssey by showcasing benthic macroinvertebrates (bugs!) that we often find during our local stream studies program, Changing Currents.

Have you ever taken a dip in a lake and come out with a tiny black or grey worm-like organism attached to you? If so, you’ve likely had an encounter with the subject of this edition of the Bug Blog, a leech! You’ve probably seen or heard about leeches before in movies or other media, but did you know that they may also live in your local stream!

Leeches can be found in the benthic environment of all types of freshwater and marine habitats around the world and sometimes even on land in tropical areas. We aren’t aware of what exactly repels leeches but some suggestions include soap, anti-bacterial products as well as salt. Not to worry though, these creatures prefer to feed on worms and molluscs and not all of them are blood sucking parasites.

Blood Suckers

Photo of a leech on a rockParasitic leeches live by sucking blood from their host organisms which range from worms to frogs and sometimes even mammals. Often leeches go unnoticed even when making incisions with their suckers to draw blood from their hosts because they release a painkilling substance on to the openings in the skin. Once they feed, blood-sucking leeches may survive over a year without nourishment because they can consume several times their own body weight in blood in one feeding.

Because these organisms provide their own form of anaesthetic, leeches have been historically used medicinally to treat diseases thought to have been caused by excess blood. In modern medicine, leeches and their blood sucking abilities are used in controlled settings to decrease swelling after limb reattachment surgeries.

How Leeches Move and Breathe

Leeches have two suckers on their bodies, one at their head and another at the rear end of their body. They use these two suckers in conjunction to crawl along substrates as seen in the video below. This is always a thrill for our Changing Currents students to see!

Leeches have no gills but absorb oxygen through their body wall, however, this does not make them intolerant of low oxygen waters. In times of low oxygen, leeches can attach their sucker to a solid surface, such as a rock, and disturb the water by waving the rest of the body, creating oxygen flow. Additionally, leeches have a high tolerance for nutrient rich waters as well as a several chemical substances, making their abundance in water systems an indicator of poor water quality.

You can learn more about Leeches and other benthos TODAY, May 13, 2017, at the EcoSpark booth at Science Rendezvous at Yonge-Dundas Square, part of Science Odyssey.

The next installment of Bug Blog will be released tomorrow, starring the crane fly!


Bug Blog is EcoSpark’s blog series in celebration of Science Odyssey, a ten-day campaign celebrating Canadian achievements in Science, Technology, Engineering and Mathematics (STEM) with hundreds of science-based outreach events across Canada for all ages. Each day of Science Odyssey (May 12-21), we will be exploring a different Benthic Macroinvertebrate (BMI), small spineless organisms that live at the bottom of waterways. These are creatures we come across all the time in EcoSpark’s Changing Currents program, where we carry out stream studies with schools around the GTA by collecting BMIs to learn about local water quality.


EcoSpark's Bug Blogs would not be possible without the support from our generous sponsor, the Natural Sciences and Engineering Research Council of Canada (NSERC) PromoScience Program.