Angry Fraggle: Champion Swimmer and Master Manipulator

There’s something moving towards you in the water. You strain to get a better look but all you see are small white specks like dust drifting about. It’s the moment when you realize that it’s not dust that you also realize your life will never be the same.

The use of a microscope confirms it: the small white specks are circles that have whip-like tails, swimming not at random, but with purpose. In fact, these 1-mm-long wormlike creatures are known as cercariae and represent just one of the stages in the life cycle of a parasitic marine flatworm called a trematode. These exotic creatures are all the more mysterious because they spend almost their entire lives inside other animals; the cercaria stage is the free-swimming one where the worm must emerge from its initial snail host to find a new host to infect. In fact, so little is known about the species that we investigated the past week that it does not even have a species name, only the working name “angry fraggle”(large)!


Screen Shot 2018-02-12 at 11.34.54 AM

Various trematode species found on Vancouver Island. How little we know about them is reflected in the lack of scientific names assigned. (Photo credits: Colin MacLeod, PhD)


Given how we value free will, one of the most fascinating aspects of parasites is their ability to modify hosts’ behaviours. For example, when similar parasitic flatworms invade cockles, they can hamper their ability to burrow into the sand which increases the chance they will be eaten by seabirds. This may be bad for the host, but it is beneficial to the parasite since they will then adopt the bird as their final host where they can mature and reproduce. (See diagram below) Interestingly, this is also a boon for a wide variety of marine life that can encrust the cockles’ exposed shells and thrive, increasing biodiversity in otherwise relatively barren mud flats.


An example of a trematode life cycle. (Photo credits:


In the lab, we exposed cercariae to various kinds of seawater with modifications to reflect human impacts on the environment, for instance including heavy metals, raising the water temperature, and increasing the acidity of the water. Most notably, we found that heavy metal pollution did not affect their swimming speed, while increasing the nutrient content of the water, much like agricultural fertilizer runoff would, decreased their speed and increasing temperature made them swim faster. In fact, the most any individual swam in three minutes was 199 mm, or nearly 20 times their body length!

As the free-swimming stage, the cercariae are the ones that will be directly exposed to and acted on by the environment. Like the salmon we have here on the West Coast, they must swim enormous distances to find home again so they can reproduce. Seeing how they will respond to a climate change and human pollution could help predict how their hosts might respond to the changing world and how that will shape the diversity and health of our oceans. Simple yet cute, repulsive yet fascinating, these worms have certainly reminded me, like Master Yoda, that “size matters not” when considering impact.

For more cool information about wacky host-manipulating parasites, check out this site:


The Circle Of Life

What do the words “Circle of life” bring to mind? Maybe you think of Simba from the Lion king? I on the other hand, think of trematode parasites.

Trematode parasites are cute (well at least I think so… you can take a look at this Wiggler  to decide for yourself) little wiggly parasites that have wacky circle of life involving three hosts.

Lets start with the parasite living within a snail. In a snail, trematodes make baby clones of themselves, which leave the snail to find the next host (a crab in this example) in the great beyond. If the trematode successfully finds and infects a crab, the parasite will chill in the crab for a while. The parasite is waiting for a bird to swoop by and gobble up the crab. Being eaten by a bird may be game over for the crab but it is actually good news for the parasite. While the bird is digesting its yummy meal of crab the parasite will actually sneakily infect the bird from its stomach. The parasite then makes eggs and sends them out into the world via bird poop. Later on if a snail crawls along and eats the bird poop (talk about yucky…) the snail will become infected (check out the diagram below for the circle of life of a trematode parasite).

Screen Shot 2018-02-12 at 8.26.55 AM

You now may be wondering why we don’t just exterminate all them trematode parasites, they sound rather gross! But they are actually super important. For Example, trematodes castrate their snail hosts (poor snail can’t make babies). Now this may sound bad, but imagine a huge snail population eating all the food on a beach (which is not great because other animals need to eat too!). If trematodes infect this population, then suddenly a bunch of snails can’t make babies and the population will stop growing as much and voila the snails are under control. Hopefully I have convinced you that trematodes are interesting (or at least important), which hopefully means I can convince you that trematodes need your help. The thing is, most people don’t know (or care) about trematode parasites, which means they get little scientific attention, so many trematodes are still undiscovered (or have been discovered and we just have no information on them at all). If you want to help us trematode people, spread the word! (For more info on why we should study parasites check out: )

Parasites, the unsung heroes

A Victim of Guinea Worm in Northern Region (see worm around the waist(

I know that picture is nasty, and my claim may sound ridiculous but humour me for a second. Look out your front window or think back to the last time you were out on the beach at low tide. Did you like what you saw? The beautiful green grass, soft in between your toes. The dizzying array of tiny things alive in and between every tide pool. Parasites are part of the reason for our beautiful ecosystems. We should be thankful for them.  Yeah you heard me right, thankful. Without these creatures our environment wouldn’t be as healthy and diverse as it is. Parasites do lots of things for us. They keep your lawn pristine by killing the larvae that birds rip your lawn is just one example. They also allow for a more diverse tidal community. They prevent shellfish from hiding in the sand allowing other organisms to live on them and attract their predators.

Now my claim may sound a little ridiculous still, but these little creatures may be another thing in the list of creatures and processes that are negatively affected by global warming. Everyone knows that our mass burning of fossil fuels is a concern for global warming,  but one consequence of our increasing release of carbon dioxide that is not as widely known is the acidification of our oceans. In our lab we investigated some of the effects of acidification and other human activity on the performance of a parasite species. While the species has not yet been officially identified, it has been affectionately nick named the large angry fraggle.

Infected Snail

Above: One of the poor snails from our lab infected with parasites that have developed and left the snail (Sam Pritchard Feb 5, 2018)

We found that acidified ocean water slowed their swimming speed. This is important because these parasites have a life cycle that involves passing between several different organisms, and if they can’t find their next host they die.

You may be unconvinced that parasites are important, and wondering why we should care about parasites dying. But there is ongoing research into the importance of parasites to the functioning of global ecosystems. More and more studies are finding that parasites are one of the key factors to maintaining the health and diversity of our globe. So even though they may make you skin crawl, the truth is that these tiny creatures play a far more important role in our environment than most people think.

If you are interested in the other ways that parasites are important, here are a couple follow up links.

Small, Mighty, and Possibly in your Dinner

Have you been feeling a little lethargic? Gaining a little weight? Not wanting to “get down and dirty”?  If so, you might just be hit with… the ‘todes (trematodes).

Have no fear though, ‘todes are actually pretty common. You would be surprised with how many animals and humans have ‘todes; hey…even your neighbour might have them! It’s nothing to be ashamed of, it just so happens these pesky little fellers are quite persistent and capable of surviving in a range of different environments. How did I get the ‘todes you ask? Well, I hate to break it to you, but you probably ate it. At this point I’m guessing you’re trying to remember when you last ate a worm-like animal for breakfast, and you’re probably thinking, how did I miss this? The thing is, the trematode that you ate was probably at a point in its life where it is extremely small in size, when it’s a “cercariae”. To emphasize how small these can be, I have included a photo of this trematode stage in one species we know as “Angry Fraggle large” (what a name).

Screen Shot 2018-02-11 at 1.57.40 PM

See those little white dots? Those are “Angry Fraggle large” in their cercariae form. A bit about cercariae, this is the stage that occurs after a trematode leaves its first intermediate host (ie. a snail). They’re basically a free swimming larva with a tail. This tail helps them disperse to find a second intermediate host (ie. amphibian, crustacean, fresh water fish, snail, etc.). There are a few ways that you could’ve ingested this parasite and eating the second intermediate host is one of them. The life history of a trematode is actually quite complex, so if you’d like to know more, check out this website and video!


Don’t worry, if you’re a human who has eaten this parasite, you have nothing to worry about. However, if you’re a snail…

Screen Shot 2018-02-08 at 10.02.20 PM


Picture taken from

This week, BIO 326 students exposed the cercariae stage of “Angry Fraggle large” to a variety of abiotic stressors associated with human activity: pH, salinity, temperature, increased nutrient levels, and heavy metal pollution. We also looked at the effect of increased glucose. The purpose of all this was to identify the stressors that negatively influence the swimming speed of cercariae. Glucose, increased nutrient levels, and pH, were the only stressors that caused a significant decrease in average swimming speed. Temperature and salinity also look like they may have negative effects, so scientists should keep looking into these!


Screen Shot 2018-02-11 at 2.00.27 PM

As a take home message today, I’d like to stress how important it is to include trematodes in your work. These guys are everywhere, so whether you’re a researcher, student, or science nerd like me, please look out for them because they could be affecting your research. For the rest of my readers out there, I encourage you to keep looking into ‘todes simply because they are a lot cooler than you think.

Screen Shot 2018-02-08 at 9.43.55 PM

Picture taken from:

Plight of the Parasites

When I say the word parasite, most you probably think of a few different words. Chances are these include “disgusting “or “revolting”. Maybe you even think of some awful picture you chanced upon while online. Maybe something like this?


Image Credit:
Or maybe something a little larger like this?



Image Credit:

If you are still reading this, bravo for sticking around! You will be happy to know that it gets much less graphic from here on out.

So, you may be familiar with the creepiest parasites out there, but parasites can actually take a wide variety of forms. By definition, a parasite is anything that lives off a host, but does not kill it. Now if you’re thinking that clinging onto someone else for food and doing practically no work sounds like a good life, you would be 100% correct. In fact, this is such a successful strategy that about 50% of ALL living species today are parasites! Okay so that may creep you out more than the pictures, but most of the parasites don’t look like the ones above, they are often much smaller like this little guy below.


That adorable little guy hasn’t be scientifically identified, but we in BIOL 326 affectionately call them ­ “Angry Fraggle (large)”. These distant cousins of tape worms, barely 0.2 millimeters long, have several hosts in their life, a common occurrence in parasites. Our “Angry Fraggle” resides in two hosts, first of which is a snail. This snail then gets eaten by a bird, which is bad for the snail, but great for the parasite as they breed in the bird and complete their life cycle.

Even though most of their life is hanging on for the free ride, these little parasites do have one stressful event, finding their snail hosts. To do this they have to swim, but since they don’t eat while outside of a host they have limited time to do so. Swim too long and run out of energy before finding a host? Game over for our little “Angry Fraggle”. This is where these parasites are running into a MASSIVE problem: climate change.

Climate change is having a number of effects on our oceans, most famously warming waters and acidification. Effects such as these can alter the energy output of swimming parasites, changing how fast and long they can swim for. This can be detrimental in their ability to reach their snail hosts, causing them to die before they reach their hosts.

You may be happy about that, but parasites are an essential part of ecosystems around the planet. Many parasites in hosts that are prey for other animals and make it easier for predators to eat them. This doesn’t just make the parasites life easier, it also facilitates a fragile balance in the system. Without parasites this balance could be disrupted, causing a collapse of this system and the death of many animals in it.Therefore, in their own unique way, parasites are vital to the survival of many species on this planet. They also serve as a strong reminder of how widespread the impacts of climate change are and how intricate the consequences will be. So next time you think of parasites, hopefully you think of how to protect them, rather than how to squish them!

If you are inspired by parasites (I will assume you are), check out this fascinating video on how parasites in human could possibly be good for our immune systems!

Why a sea star should consider retiring in Florida

Picture this: sunny skies, white sand beaches, palm trees galore, and shuffleboard to your heart’s content. Okay, it may be hard to imagine a sea star enjoying these activities, but there is one thing that sea stars should try to do: escape the cold!

source GIF:

Sea stars are ectotherms, which means they depend on their environment to regulate their body temperature. Some cool tricks that sea stars do to help prevent their bodies from drastic temperature changes is to become bigger! For example, when the common purple sea star experiences temperatures that are too hot for its liking during low tide, it will actually take in extra water into its body during high tide. That way, it’ll be harder for it to get too hot again because it’s so much bigger! This is called increasing the “thermal inertia.” Just imagine trying to heat up a large pot of water versus a tiny cup of water. The larger (unwatched) pot will take longer to boil.

On the other hand, it also turns out that some sea stars actually can’t live their best life if it’s too cold out. One species we looked at in particular is the mottled star, or if you want to impress your colleagues, Evasterias troschelli. Let’s take a look at some reasons why the mottled star should consider retiring in Florida. 

Firstly, the issue of righting-time. Imagine you are placed on your head; naturally, you’d want to stand right-side up, right? Well, for sea stars, if they are placed on their backs with their stomach exposed to the world, they also want to flip around. However, if sea stars are found in an environment that is colder—say, -4ºC— than ideal, which is about 12ºC, it actually takes them longer to flip right-side up. When they’re not firmly attached by their tube feet, that’s extra time to get picked off by a seagull! Here is a step-by-step guide of one way a sea star can flip over, if you want to practice it yourself at home.



Colder temperatures also affect a sea star’s feeding pattern, as we saw that mottled stars kept in colder waters took longer to eat mussels, some of their favourite foods. We put some mussels at one end of a tank and a mottled star at the other end, then measured the time it took to first touch the food and also to start eating it. The sea stars kept in colder water conditions took longer. I don’t know about you, but when I see my favourite food, I make a beeline to eat it as soon as humanly possible, especially if it’s cold out.

Considering the negative effects cold temperatures has on sea stars, I suggested Florida as a possible retirement place for them to consider. However, recently it seems that Florida might be getting too cold for ectotherms too. If cold stress on sea stars interests you, take a look at this article from the Washington Post that shows iguanas (also ectotherms) literally freezing and falling off trees in Florida! Or if you’re more interested on possible effects of rising temperatures, check our this article on Sea Star Wasting Syndrome featuring our very own Chris Harley.

Judging by all the things that could happen to sea stars in a changing world, it’s fitting that I end with this picture. Let’s pray for the future of sea stars shall we.


Picture: taken by Bessie He 2018

Can you survive the Sea Star Apocalypse?

I’m sure you’ve seen protagonists overcome zombie apocalypses in movies but do you think you would be able to do it? Well currently we are experiencing a sea star apocalypse and it started back in 2013 along the coast of Washington State. You may see arms laying on the shore that were once part of a healthy sea star, some too far gone that they are unrecognizable. Sea stars are losing limbs and swelling up; eventually dying from a mysterious wasting syndrome. This disease has been spreading across North America especially from Alaska to California. The agent causing this syndrome is a virus, killing the host including species Piaster ochraceus and Pyncnopdia helianthoides, resulting in a decrease in the sea star population.

What can we do stop the sea star apocalypse? Well we need to figure out what factors could have caused the virus outbreak. Recent studies have shown that as temperature increases viruses will also grow and reproduce to make more copies.

In our Biology 326 lab, we decided to investigate the effect of temperature on Evasterias troschelii. We examined how cold temperatures during low tide has an effect on the performance such as feeding rate and righting time. We used three different temperatures to test these behaviours and predicted that behavior is slower in cold temperatures compared to warm.

We placed sea stars in cold to warm temperatures. We predicted that righting time is slower in cold temperatures compared to warm. Our experiment shows that sea stars take more time to flip in warmer temperatures than cooler.

Screen Shot 2018-02-05 at 5.46.24 AM

Evasterias Troschelii flipping over. (Photo credit: Jessica Dhaliwal)

When testing the effect of temperature on feeding rate, we predicted that feeding rate is faster in warmer temperature. As predicted we found a faster feeding rate at warmer temperatures compared to cold temperatures.

Temperature could be a factor that is responsible for the sea star apocalypse. Climate change is causing an increase in temperature resulting in a suitable environment for the virus. There could also be other factors that are causing the spread of the wasting syndrome. We need to investigate more factors in order to stop the decline of sea stars.