Bug Blog #7: Crayfish: The River Lobster

Date: May 18, 2017 Author: EcoSpark Categories: Latest

Welcome back to our seventh edition of Bug Blogs, celebrating Science Odyssey by showcasing benthic macroinvertebrates (bugs!) that we often find during our local stream studies program, Changing Currents.

In this installment of our Bug Blog series we will be exploring the crayfish. If you have ever spent time on the river’s edge you have probably spotted these lobster-looking critters. Compared to other benthos, the crayfish can grow to be quite large, anywhere between 4 to 16 centimeters! Your first question is probably this: can I eat them? The answer is yes! Crayfish are enjoyed in a French dish called écrevisse and are prepared exactly like lobster.

Crayfish can be found in streams, lakes and ponds throughout the world. Over 500 species have been found to date with over half found in North America. Crayfish enjoy living in rocky or weedy shorelines at an ideal depth of two meters. While these are ideal conditions, crayfish can be found in most aquatic environments at a depth of up to thirty meters.

Source: CAM Jr.-Sr. High School/BGSD

Life Cycle

The beginning of a crayfish’s life begins tethered to the mother. Eventually, the young crayfish will shed its skin and lose the physical connection to the mother. Crayfish have a fairly short life, reaching adulthood after shedding their skin 6 to 10 times and living up to two years.


Crayfish play an important role in the food chain both as predators and as prey. Because of the large number of predators which feed on them, crayfish have several cool defensive mechanisms. The first and most obvious are their large claws.  These can be used to fend off smaller predators and to handle food. The crayfish’s first three sets of legs are also clawed and serve a similar purpose. Next, while crayfish often crawl around on the bottom of streams or ponds, they also have a fan shaped tale which they can use to quickly escape from slower predators. When swimming, these guys can move very quickly. Crayfish use their tails to propel themselves backwards instead of forwards like most aquatic species tend to do. Lastly, crayfish have the ability to break off their own legs when trapped by a predator in order to escape. Have no fear! The crayfish can regenerate the lost limb later in order to continue its nightly routine of eating and crawling.

What Do They Mean?

So what do crayfish indicate when assessing water quality? Crayfish have a tolerance value of five meaning they are right in the middle of the scale. Crayfish are fairly tolerant to pollution and temperature which explains why they can be found in such a wide variety of habitats. While they are one of the more interesting species of benthos, they do not necessarily indicate good quality water. When found in the field during EcoSpark Changing Currents sessions, crayfish often get their very own bucket and are given fun names before being released at the end of the day.

A crayfish found during a Changing Currents program at Rouge Park.

We’ll see you back here tomorrow to learn about everyone’s favourite, the dragonfly!

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.