A chance encounter with a dead Slow Worm on a lane in the Burren led to Nick Parry’s six-year quest to understand this mysterious reptile
The mysterious slow worm is a species of legless lizard with a snake-like appearance and the Latin name of Anguis fragilis which means fragile snake. This is an apt description as they are able to discard a part of their tail as a form of defence if attacked. They differ from snakes in that they have eyelids as do all lizards whereas snakes do not. They generally grow to a maximum length of around 46cm. Thought to be the longest lived of all lizards, slow worms are widely distributed throughout most of Europe and are common in the UK but it was 1913 before they were first reported in Ireland.
Since then there have been numerous reported sightings throughout Ireland though these were mainly attributed to escaped animals introduced through the pet trade.
The first reported discovery of slow worms in the Burren was made in 1972 by Seamus Kelly and published by the late Dr T.K. McCarthy of the Zoology Dept, UCG, in 1977. Two slow worms were found by Mr Kelly and according to Dr McCarthy were probably mating. They were both at least 32cm long and Dr McCarthy measured one, the male, at 34cm.
Slow worms are cold blooded but unlike the common lizard which prefers to recharge its body heat by receiving the direct rays of the sun, slow worms tend to take refuge under the cover of sun warmed objects such as stones and wood.
They will also use scrap items as refuges so should suitable materials be placed in appropriate positions any slow worms in the area may utilize them. Pieces of corrugated tin and hardboard are effective for this purpose as are bits of roofing felt, planks and even offcuts of carpet. In my experience, ant colonies form almost immediately after a cover is positioned and it is common to see a slow worm, apparently resting peacefully and unperturbed while lying in amongst a roiling mass of ants. Being semi-fossorial (habitual burrowers) slow worms spend much of their time underground or deep in vegetation especially during bad weather or when hibernating. Feeding mainly at night on slugs and insects, they can exist in gardens and populated places with their secretive and enigmatic habits going undetected.
With a lifetime interest in reptiles and amphibians, the chance finding of a dead slow worm on a lane at Derryowen townland during the summer of 2012 brought to memory the vague mentions I had heard of a slow worm colony in the Burren. That fascinating looking reptile, a male of around 35cm even with a squashed head, made such an impression on me that I resolved to try and find them.
At the end of August 2015, I began by placing a 50cm square of corrugated tin at the base of a dry-stone wall. Approximately 100 metres away, also next to a wall I placed a similar sized steel sheet. During the first week of September I returned and not very hopeful, was surprised to find a beautiful healthy slow worm under the corrugated tin, a female of about 35cm length which I photographed. Every few days after that I returned to check the covers and by the time hibernation had probably occurred in mid-October, I had encountered 13 slow worms. All were found under the tin and nothing under the steel sheet.
Studying the photographs, I could see that twelve were females and one was male. It also became apparent that those thirteen encounters were of just three animals. Female one was seen on nine occasions, female two three times and the male just once.
Those initial sightings sparked an interest that set me on a path of study that is still continuing.
I wondered if the cover was left in place into next spring whether the same slow worms would return. I also considered whether the ratio of two females to one male was usual and why the females appeared more often than the males.
Over the winter I read everything I could find about slow worms and by early spring 2016 I began a serious slow worm hunt. With permission from landowners I placed covers in other townlands whilst the original two covers remained.
All covers were checked two to three times each week and the site for each one was carefully selected. Covers were placed next to structures such as dry-stone walls or thick hedgerows or deep into bramble patches, places where slow worms would feel safe and enable them a quick exit to dense foliage or other shelter if disturbed. By the end of summer 2016 my total encounters for the year numbered 120.
Using these placed refugia my aims were to encourage slow worms to reappear in the same place and also to discover the extent of the area they were inhabiting.
In 2017 I left in position some of the covers previously placed but moved others to outlying areas. The covers were mainly of corrugated tin but also tin sheet and carpet.
In consequence of this change the results for 2017 were disappointing in that there were just 56 slow worms encountered. However, some of these were repeat sightings from previous years and new townlands were found to be inhabited. I was still photographing all slow worms and was able to identify various individuals by their unique head and neck markings. Females were found in numbers but males remained a rare find. To limit disturbance and distress to the animals, no slow worms were ever handled.
The same tactics were followed during 2018 but with the number of covers increased and the addition of some new materials which now including corrugated bitumen, squares of roofing felt, steel sheets, carpet and hardboard along with corrugated tin.
Further townlands were targeted with some covers remaining in their original positions as before. 2018 brought me success with a total of 150 encounters. Females continued to outnumber males and certain individuals were being seen for the second and third years and under the same covers. These discoveries were remarkable and excitingwith the probability of a home range, for females at least, seeming likely.
During 2019 I had a total of 38 covers placed in a variety of townlands and although many covers failed to produce any slow worms I ended the year with 404 encounters and with as many found in townlands in County Galway as those in County Clare. My failure to find any slow worms in certain areas did not mean they were not, or had never been there.
Repeated sightings were often irregular as it might be weeks, months or even into the following year between findings of certain individuals but the probability of a home range was further enhanced when in early 2019 a female slow worm was discovered under her usual cover, a tin sheet, for the fourth successive year.
My results were interesting with regard to sex ratios too. Most studies detailing sex ratios generally reported two females to each male. However, I was finding up to as many as nine females to each male every year. The only previous study in the Burren was in 1999 by the NPWS who reported 31 females to 18 males.
I have found a number of individual slow worms on numerous occasions and over several years. I have seen them mated, the necks of females damaged through the aggressive biting and gripping by males in the lengthy mating process. I have watched those females swell dramatically as the baby slow worms developed. I have seen them slim again having birthed and tiny gold and silver slivers of a mere 80mm length appear around the site and those tiny slow worms, some with their birth markings still identifiable doubling in length by the following autumn.
Many adults would measure over 30cm with the longest I discovered being 43cm. By the end of 2019 my total Burren slow worm count numbered 743 along with a mass of relative data.*
I have no doubt, bearing in mind their secretive behaviour that slow worms have long resided in the sparsely inhabited wilderness of the Burren area even though they have gone largely unnoticed. I have spent six years now actively seeking them out and have found only six in the open. Of the twenty-four townlands sampled to date I have discovered slow worms in twelve of them.
There is a flourishing slow worm colony in the Grange area of Mullingar with many sightings and reports which has been common knowledge locally for many years. Perhaps there are others too.
As to whether they were introduced or are native there is no evidence either way but if they were introduced it must have occurred many years prior to the 1970s.
To learn more about Nick’s research, see:
A study of the present state of an Irish colony of the Slow Worm, Anguis Fragilis Linnaeus, 1758) in the Burren Counties Clare and Galway 2015-2019. Nicholas Parry, Bulletin of the Irish Biogeographical Society No 44 (2020)
About the Author
I was born in Liverpool 73 years ago and always had an interest in nature. My earliest pets included frogs, toads, snakes and lizards. Possibly due to my sporting activities, coupled with my outdoor interests, I left school with little to show for my time there. But my interests continued, with a particular fish species playing a major role. In pursuing that fish, I realised that there are so many variables and idiosyncrasies with wild creatures, that even someone considered an expert cannot know everything. Data collection became of value. I systematically recorded such details as air and water temperatures, capture times, signs of feeding activity, barometric conditions, bait and techniques used. Although the methodical recording of data was useful, determination and persistence was pivotal to any degree of success.
Discovering the Slow Worm gave me the new challenge of learning what I could about this little-known colony. My data collecting resumed, but this time with reptiles. Between February and October, I spend my days in the Burren area, seeking out these fascinating creatures. It is often the very last distant place, when I am really tired and have discovered very little, that produces the most significant result of the day, month or even year. Regardless of the slow worms I find, observing the hum of life in the Burren is a perpetual joy of which I never tire.
I could never have imagined that a project started purely out of personal interest, and with no academic training or experience, would have resulted in a research paper published in a scientific journal.
As long as you have interest, enthusiasm and tenacity, anything is possible.