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Studying the barred grass snake in England, a dream come true

This article was contributed by Save The Snakes Advisory Committee Member Steven Allain.

In this blog, Steven introduces his PhD research on grass snakes and how snake research can help us in understanding them better

Ever since I was a young kid, I’ve wanted to work with snakes for a living.

It was a combination of spending every waking hour I could in the outdoors and watching a number of influential presenters on TV (such as Steve Irwin) that really ignited this passion. I’ve spent the past seven years working with amphibians, with reptiles taking the back seat. Now, this has been flipped on its head although I am I still involved with a number of amphibian conservation projects around the world. In this introductory blog, my goal is to give you all of a picture of my current research project and where I think it is going to lead in the future.

Until recently the barred grass snake (Natrix helvetica) was classified as a subspecies of the more wider-ranging European grass snake (Natrix natrix). This was until in 2017, after some investigation into the mitochondrial DNA of different populations of grass snakes across Europe, that N. natrix was split into a handful of species. In this case, a small number of subspecies were elevated to species level including the grass snakes found in the UK. It’s important to note this as all of the literature that focuses on grass snake research across England and Wales (where they are found most predominantly in the UK) prior to this taxonomic split classes them as either Natrix natrix or Natrix natrix helvetica. As you can imagine, this has caused quite a few headaches but at least they have been easy to resolve. This isn’t the case for areas such as west Germany where there are now populations of more than one species of grass snake.


Fast-forward to the present day and I’m studying the barred grass snake for my PhD in Biodiversity Management. Despite the fact that the species has a wide distribution across Western Europe and is relatively widespread throughout its range, we still know very little about it. It’s almost as if the snakes have been neglected by herpetologists over the years as they were too busy working on the exotic species that were being brought back to Europe as colonial empires were being expanded throughout the preceding centuries. This large knowledge gap has been open for some time and although researchers have been working to fill in the blanks since the late 1800s, there are still many for me (and others) to work on.

For example, the snakes are semi-aquatic and therefore are often stated as feeding primarily on amphibians. However as anyone who studies amphibians knows, they aren’t available all year round – especially in a temperate climate. You have the adults returning to ponds to breed in the Spring before leaving shortly after. There is then a short period of time between which the eggs hatch, the tadpoles grow and then metamorphose. It is at this time when there is a lack of food around that I’m most interested in. I suspect that the snakes are feeding on the many small mammals (that like to share the same refuges as themselves) as well as opportunistically feeding on fish and small bird species. I’m hoping to investigate this further by collecting grass snake faeces and testing for the presence of prey DNA to figure out once and for all what these snakes are eating. I feel it must be stressed here that not every population will feed on exactly the same thing due to differences in prey availability, but expanding the known food items of grass snakes will be valuable in the long run.

Another area where our current knowledge is lacking is that of population dynamics. Thankfully the life cycle of barred grass snakes has been studied in detail so we age and sex individuals on size and other morphometric characters. We also know the time of year the snakes lay their eggs and when to expect their hatchlings to emerge. What isn’t known is where the snakes prefer to lay their eggs. Most of the rural land in much of Western Europe has been converted to agriculture which means there are plenty of compost and muck heaps for grass snakes to lay their eggs in. If this source of decomposing material wasn’t there, where would the snakes prefer to lay? Due to the snake’s reliance on this source of man-made nesting sites, are they completely dependent on us? I don’t think I’ll be able to answer these questions during the time of my PhD but they are certainly some that I’d like to work on in the future if at all possible. Think about it this way, a very subtle change in how we manage farmland waste could cause a drastic decline in grass snakes across Europe. It’s only speculation for now and more evidence is needed but I urge you to watch this space!


Another area I’m studying in the population I’m intensively monitoring is the presence of snake fungal disease (Ophidiomyces ophiodiicola). It has previously been confirmed to be present at the site by the use of genetic tests but this is only half the story. In order to confirm infection with snake fungal disease (which is now known as ophidiomycosis) you need to twin genetic techniques with histological ones. Most of the snakes I’ve been capturing and collecting biometric data from have been healthy with no signs of infection. There are a few snakes however that do have limited lesions, although these may be explained by infection by another fungus (or even a bacterium) as the clinical signs are not unique to ophidiomycosis. I aim to keep a very close eye on this in the coming years but for now my main focus is determining how the population functions as a whole, what the snakes are feeding on and what affects their distribution. All of this information can then hopefully feed into both practice and policies to help safeguard the species for perpetuity.

If you’d like to follow my updates from the field or just look at some beautiful photos of some snakes, then please check out #CranwichSnakes on Twitter and Instagram.


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