IRELAND'S REPTILES | Serpentia in Absentia:

Why There Are No Snakes in Ireland

Every year, when Saint Patrick's Day is just around the corner, all the old tales that are part of the legend surrounding Ireland's most famous saint are retold, reviving this story in the minds of older generations and introducing it for the first time to the young. Although it has long been known that many of the elements in the popular version of St. Patrick's life do not accord with what we know of him as a historical figure, the myth of St. Patrick has lost none of its power and remains a cornerstone in the culture of Ireland. However, there is one element of his story which seems to have arisen due to an all-too-literal interpretation of the impact his arrival had on ancient Ireland, and is popularly used to explain why Ireland lacks one particular group of animals – snakes.

According to the legend, when St. Patrick returned to Ireland as a missionary, among his many acts was to banish all the snakes from the island. This odd aspect of St. Patrick's story only makes sense when we realise that, in the past, paganism was often represented as a serpent, so the story of St. Patrick ridding Ireland of snakes really stems from him ridding the island of paganism by converting the Irish to Christianity.

But even if we know that St. Patrick isn't responsible for their absence, we are still left with the question: why are there no snakes in Ireland?

Once upon a time, snakes very likely did live in Ireland. Today, the island has only one native reptile, Zootoca (formerly Lacerta) vivipara, the common or viviparous lizard – which gets its name from the fact that it gives birth to live young rather than laying eggs – but in the distant past Ireland was home to a far greater assortment of reptiles.

Around 55 million years ago, Ireland was a much warmer place than it is today. This was a time when the whole globe was experiencing a greenhouse climate with average temperatures that would eventually reach around twice as high as those of our modern world. Alligators prowled waters well inside the Arctic Circle, while temperate forests there played host to a variety of life-forms, including tapirs and banana-like plants. Antarctica too was bedecked in temperate and near-tropical forest and populated by everything from sloths to marsupials.

Ireland lay in the midst of a great band of subtropical forest which stretched from around 30 degrees north to 60 degrees north. Sitting at a latitude of around 40 degrees north, about where the Pyrenees stand in our modern world, Ireland was around 10 degrees more southerly than it is today (the island's most southerly point, Mizen Head, occupies a latitude of over 51 degrees north). The global climate, coupled with its more southerly position, ensured that Ireland could sustain a far more exotic fauna than it can today.

Although Irish fossils from this period are very rare, we can infer the presence of many animals from the far richer fossil record of Britain, as there is evidence to suggest that these two lands were joined together at this time.

Thus, this ancient Ireland was likely home to a variety of different lizards, crocodiles, and snakes. Indeed, there are far more fossils of snakes from some sites in England dating from the late Eocene (c. 38–34 million years ago), and, what is more, these appear to have been boas, making them relatives of the boa constrictor which is found today in North, Central, and South America, as well as some Caribbean islands. So, such ancient boas may well have slithered, hissed, and hunted in Ireland at this time also.

For many millions of years, then, Ireland maintained a rich fauna of reptiles, but as the global climate became progressively cooler, this ancient land became less able to sustain the presence of many of the more temperature-sensitive groups, such as the crocodiles, which are today not found any farther than 30 degrees north or south of the equator.

However, this does not explain the absence of snakes in Ireland, as they are far less dependent on warm temperatures than their crocodilian relatives, and, in fact, there are a number of snake species found in Britain today. Furthermore, as noted in an article by Michael Viney, a long-time journalist for The Irish Times, around this time last year, one of the species found in Britain, the European adder (Vipera berus), is also found in lands inside the Arctic Circle. Thus, as Viney states, 'There is no climatic reason why the European adder should not flourish in the Ireland of today.'

At this point, it might be understandable if one or two people raised their hands in objection to state that they have seen snakes with their own eyes in Ireland, while walking in the Burren. However, as Viney notes in his article, these snake-like creatures are not true snakes but legless lizards called slow-worms (Anguis fragilis) and, in any case, they are only recent arrivals on the island, their presence first noted just over four decades ago, in 1977.

The absence of true snakes in Ireland today is likely due to events which occurred far deeper in Ireland's past, towards the end of the last Ice Age. At the height of the ice sheets' extent over Ireland, around 24,000 years ago, the whole island would have been covered, in places over a kilometre deep, and the only life-forms to survive this glacial siege were possibly plants which survived on nunataks, or rocky outcrops peaking above the surface of the ice. Snakes, then, as well as all other animals, would not have been able to survive in Ireland at this time.

When the ice sheets subsequently melted and warmth returned to Ireland once more, the sea seems to have risen too fast to allow snakes to invade. As Viney says, snakes 'simply hadn't slithered north fast enough to beat the resurgence of the sea.'

It is Ireland's early transformation into an island, by around 16,000 years ago, then, that is responsible for its lack of snakes. The ancestors of Britain's snakes had far more time to invade that land, as Britain was not finally cut off from Europe until around 8,000 years ago, when the ancient landmass called Doggerland connecting it to the continent was dramatically submerged by the sea.

So, the mystery of Ireland's missing snakes appears to have been solved, but no doubt the legendary tale of St. Patrick will endure. Having coiled itself tightly around the Irish imagination, it has held it in an unbreakable grip, sinking its fangs deep into Irish culture.

Note: The first part of this blog title has been borrowed from a 2012 paper by Dr Declan Quigley: 'Serpentia in absentia: an historical review of snakes in Ireland.' Lacerta 4 (3), 6–18.