Freshwater Exploration: are Invasive Crayfish Predating Benthic Invertebrates

This week Dispatches from the field welcomes Arron Watson,  who conducted his masters by research in Entomology at the University of Reading. His summer project was to investigate how signal crayfish, an invasive species, has an impact on benthic invertebrate predation. He sampled 20 sites across the UK, 10 without signal crayfish, 10 with. He conducted this field work over a month in May and is telling us about his experiences here!

May 1st 2018: the first day of field work for my summer thesis, a key part of my MRes in entomology at the University of Reading. I had already spent roughly six months planning my field work, and decided that I wanted to start my freshwater exploration in Scotland. My supervisor from Buglife, Scotland is based in Stirling and he had offered to show me some advanced insect identification techniques. Next, I would drive over 1000 miles around the rest of the U.K. in my 1997 Nissan Micra (aka “the beast”), stopping over in a mix of locations including a hotel and the houses of friends I had met in my previous life as a back packer.

“The beast”

I left Reading at 6 am and headed north up the backbone of the country towards Scotland. I have lived in Reading for about 3 and half years now, so I have gotten used to the urban way of life. In Reading, I see buses much more often than I do trees or sheep. But driving along on a beautiful day with a wad of CDs was fantastic, and the closer I got to Scotland, the greener the landscape appeared and the more free I felt.

I met Craig (my supervisor) in Stirling. He suggested getting some rest after my 7 hour drive, then setting out first thing tomorrow for a set of four rivers to start my sampling. If you’ve never had the chance to “kick sample” before, it’s a lot of fun. It’s one of those things that takes you back to being younger: standing in the middle of a flowing river, dipping your net in, and waiting for living things to end up in there. When you remove the net from the river and you see lots of things wiggling about, you think, excellent!

After collecting the samples, the next step is to sort them. This is where the skill comes in: not only do you have to remove the things you don’t need (such as fish), you also need to identify things based on differences in morphology – without books, depending only on your memory. But Craig also told me just how many different stone flies and mayflies there are, and explained that I wouldn’t be able to tell them apart just by eye, so I should be strict if I thought I collected everything.

Luckily for me, I already had experience identifying terrestrial invertebrates, which was a huge advantage, so after a day’s training, I was a professional picker. Now my task was to collect samples from the rest of my sites, spread across the UK. I would spend the next 3 weeks having limited contact with anyone other than my hosts at each accommodation.

Kick sampling methods used by the environment agency.

My next set of sites were on the Clyde river in Scotland. I was informed to take a letter with me to show any catchment officials or anglers I had permission to be there. I arrived at my first site and started to get a feel of what it was like to be in the middle (not literally) of Scotland. Water running fast, no one in sight, greenery everywhere: bliss! As I got to the edge of the riverbank to look at my first GPS location, I took a minute to stare at the flow of the river and thought, “Oh! Actually that looks like it’s flowing quite fast.” I looked around and realised I really was alone. This is where you start to build field work skills, I realized: no one to rely on, no one to ask, “do you think I will get swept down the stream?” – just your skills and intuition to rely on. After a moment of worry, I told myself, “OK, if I go down that river, I have my buoyancy aid and an inflatable bag which has my phone in it, so I suppose I would be noticed flying down the river like a game of ‘pooh sticks’” (look it up!). I used the pole of my kick sampling net (approximately 1m) to gauge the depth of the river, chose an area where the flow broke slightly, and stepped in. Within a short space of time I had picked my samples, and off I went to Edinburgh to see an old friend. We had a few beers and the following day I headed down to East Yorkshire.

“Alone!, bliss”

I started to feel like things were going really well. My samples were being kept cool in ethanol, the car was running well, and there were no issues so far. It wasn’t until I arrived in Norwich a week later that I would experience my first major problem – which really couldn’t have been controlled or pre-empted.

I had driven to Kings Lynn, heading for a river at the bottom of some farmer’s fields – which was nothing unusual. I found the location and got ready as usual: throwing my waders on, connecting the buoyancy aid connected to my belt, and grabbing my net. As I started to walk down the road, out of nowhere a farmer’s truck drove past me with a carriage of cows. It didn’t faze me at the time: I just headed down the side path, eventually reaching the field with the cows and calves. I walked up to the fence, intending to climb the gate and walk across the field…when all of a sudden, the cows started marching over to me. I had a strange feeling they weren’t there to welcome me.

By the time I got to the fence, a large gang of protective female cows were gazing at me. I tried to spook them, but they wouldn’t budge: they simply grunted at me, looking quite angry. I thought, “No chance am I getting trampled by cows during field work! I will just go around, because there’s another field next door.” I started to walk around to the side, watching the cows follow me out of the corner of my eye. I jumped the fence and started to make my way through some bushes (and brambles), regretting this choice but at the same time pretty sure it was better than cows trampling my head.

But suddenly…squelch! My height dropped by about 2 feet: I had sunk. It turned out that the way I wasn’t meant to go was some sort of swamp or bog…either way, I was stuck. This had happened to me once before, on Cleethorpes mudflats as a young lad. That time, I had gone out in brand new trainers my mum specifically asked me not to ruin. I looked at the cows and thought, “Ha! Cows 2- me 0.”

At this point getting out was my main focus. I knew that when in mud like this, you need to expand your surface area in order not to sink. Unfortunately for me, this meant laying on my front and crawling out. I moved across the marshy land like a seal that had lost its way, until I finally made it out. At times like this, you either have to cry or laugh. I chose to laugh…until I left and realized that the cows were waiting for me like a trained animal retrieving a stick!

“2-0 to the cows”

I will leave you with the image I saw at this point, and I’m sure you can guess what happened next…squelch!

Field work offers rewards and excitement no other work can sometimes……Let’s not forget the cows!


Arron is trained in field ecology, and has worked on a number of different research areas such as entomology, freshwater ecology, bat ecology, and the use of drones. He conducted an ecology and wildlife conservation degree at the University of Reading, went on to complete my masters by research in Entomology there also. He is currently working as a research assistant at the University of Reading and founder of a UAV consultancy called EcoDroneUK. 

There must be something in the water

Please join us in welcoming Cheryl Reyes to the blog this week! Cheryl, a recent graduate from the University of Waterloo, is currently working as a Conservation Technician with the Nature Conservancy of Canada. For more about Cheryl, see the end of this post.

Although I have been working at a land conservancy monitoring alvar and tallgrass prairie ecosystems, and managing invasive plant species for the last few months, one thing remains the same: when I stumble upon a river, wetland or small creek I always wonder, “what kind of benthic invertebrates are living there”.

This recurring thought stems from my first true interest in the field of ecology: water and benthic macro-invertebrate sampling.

Sampling benthics often means going to very beautiful places sometimes in the middle of nowhere.

Benthic macro-invertebrates are aquatic insects that live at the bottom of water bodies, such as aquatic worms, leeches, beetles and flies. They do not have a backbone and are large enough to see with the naked eye, but when you put them under a microscope for further analysis they look much more impressive! These little creatures can reveal a lot about the health of a freshwater system because they are an important part of the aquatic food chain and respond quickly to stressors such as pollution. For this reason, they are referred to as “indicator species”.

One of my favourite photos of a mayfly larva, from the Ephemeridae family. You can distinguish mayfly larvae by their side gills and three (sometimes two) tails. This one has tusks on its head!

I was first got introduced to benthics during a field ecology course at the University of Waterloo. Since then I have collected and identified benthic invertebrates for many organizations, most recently during my role as a Monitoring Technician at the Crowe Valley Conservation Authority. Crowe Valley runs a benthic monitoring program within their watershed to monitor water quality. Sampling sites are located throughout the watershed and benthics sampling follows the Ontario Stream Assessment Protocol (OSAP) and the Ontario Benthos Biomonitoring Network (OBBN).

Sampling for benthics is fun and easy to do. Dressed in waders, with a net in hand, two people get into a stream and move between the banks while kicking up the substrate on the bottom. The net is swept back and forth through the water to collect benthics. The continuous sweeping motion is important to prevent any benthics collected from swimming out of the net. After three minutes of kicking and sweeping, the contents of the net are emptied into a bucket and hauled back to the lab/office for identification.

Me sampling for benthics. This was a great day because it was the only day of the entire field season I didn’t have to cover my face to protect myself from the bugs.

However, as is the case with most field work, sampling for benthics is not always the most glamorous job. Sometimes you get so into the Footloose-esque substrate kicking that you forget to watch your footing and trip over some large rocks, a log, or if you’re lucky (or unlucky) a large snapping turtle. Other times you wish the three minutes of kicking would be over because you can feel the sweat pooling in your waders. Much of the time you can’t see a darn thing because you have your bug jacket on to prevent all the mosquitos, black flies and deer flies from devouring your flesh. And when you look at the contents of your net, it’s hard not to wonder, “Are there actually any bugs in this giant pile of mud, rocks and leaf litter??”. But the most draining thing is hauling your large buckets and equipment to the site, then hiking the full buckets out from isolated locations after a long day’s work…then enduring the frequently lengthy drive back to home base.

My work station for 8 months at the Crowe Valley office. During my undergraduate, I was used to identifying bugs in a laboratory setting. But while working at Crowe Valley, I had to use ingenuity to set up a functional work station!

Studying benthics is definitely its own realm of ecology, with its own fieldwork quirks, and I love it. Why? The reward is always great. When you find benthics in your bucket and put them under a microscope, you get a sense of how complex aquatic ecosystems really are. I could spent hours looking at all the different taxa and the features that make them truly unique specimens. And because they tell you about water quality, studying them allows you to begin to appreciate how important water is in our everyday lives, and why it’s essential that our ever-developing society conserves and protects freshwater ecosystems.

So next time you see a body of water, remember that there is a little universe lurking in the depths of the substrate. All you need to discover it is some waterproof footwear, a container and a net.

Caddisfly larva from the Hydropsychidae family in the palm of my hand. This taxa, as a member of the Hydropsychidae family, spins nets that help it catch food such as algae, leaf litter and smaller benthic invertebrates.


Cheryl Reyes is a graduate of the School of Environment, Resources and Sustainability at the University of Waterloo. Her undergraduate research focused on assessing the benthic invertebrate communities of restored streams in urban areas. She is currently working as a Conservation Technician for the Nature Conservancy of Canada.