St.Patrick, the Ice Age and herpetology

Viviparous lizard

The study of reptiles and amphibians is called herpetology. In Ireland, unfortunately, it is a limited field – apart from the occasional sea turtle, we have only one species of native reptile, and just three amphibians. Some might blame, or thank, St. Patrick for banishing snakes and other poisonous creatures from these shores. But of course, it was the last Ice Age, not Patrick, that was responsible. 

From about 115,000 to 24,000 years ago, Ireland was covered by ice. Then the Earth started to warm up and the ice to melt – by 20,000 years ago, West Cork would have been part of an area of tundra, like Lapland or northern Siberia today, running from Donegal, along the west coast, south to Brittany, and from Cornwall to Denmark. Everything to the north and east was still frozen. 

As the ice retreated, the sea level rose. At the same time, animals that could tolerate cool temperate climates migrated northwards. The last creatures to reach Ireland from Britain possibly came via land bridges, but once those were submerged, 12,000 years ago, only birds or bats were going to get here under their own power. Britain, however, was still attached to mainland Europe for another 4,000 years, giving more species time to move in. 

Snakes are poikilothermic (cold-blooded) and need heat to be active, so they were slow to colonise newly defrosted landscapes. Only three – the grass snake, the smooth snake and the adder – managed to get to Britain; none made it to Ireland. 

Fear of snakes – ophidiophobia – is one of the commonest aversions people have to animals, understandably so. There are approximately 3,900 species of snakes; 600 are venomous, and about 50 are dangerous to humans. The adder is the only venomous snake in Britain, though its bite is rarely fatal. But in Asia and sub-Saharan Africa, thousands die from snake bite every year – 1.2 million in India alone in the last twenty years.

 The first wild snakes I ever saw were in Zambia on school field trips – a large cobra, dead on the road, and a black mamba, the most feared of all African snakes, alive and hissing in the washroom. The manager of the lodge where we stayed shot that snake, and I took it back to school in a large jar filled with gin. On another occasion, beside Lake Malawi, I watched as a crowd chased a black mamba and beat it to death. It was sad to see, but black mambas are large, aggressive if threatened, and their neurotoxin highly potent; a bite, far from hospitals with anti-venom, is nearly always fatal. 

Also in Malawi, while carrying out a survey of frogs in a nature reserve, I came upon an enormous python moving slowly along a sandy path. Pythons are not venomous; they rely on strength to constrict their prey, and extremely elastic jaws to swallow it – one of our geese had already been a victim. This python was like a bronze and silver telegraph pole – I just had to take a photograph of it. But by the time I had fitted the correct lens, the snake was already heading off into the grass. So I did a crazy thing – I grabbed its tail and tried to pull. The power of that snake was incredible, and I couldn’t stop it gliding off into the undergrowth. I might not have been able to do much had it wrapped itself around my legs and swallowed me whole. 

 Snakes evolved from lizards in the late Cretaceous Period – four fossil snake species from that time had small back legs. Pythons still have little claws, the remnants of these limbs; they are used now to grasp their partner during mating. Some lizards, such as skinks, have lost limbs more recently in response to a burrowing lifestyle, so while there are skinks with four normal legs, other species have four reduced legs, two legs, or no legs at all. 

 Unlike snakes, lizards have eye lids and ear openings, and only two of the 7,000-odd lizard species are venomous. Large lizards, such as the Komodo dragon, might be rather scary, but most are handsome, inoffensive creatures. Around fifty species live in Europe, mostly in the south; three are found in Britain, and one in Ireland – the viviparous lizard. This is small, brown and speckled, and unusual among lizards in that it gives birth to baby lizards, not eggs. Lizards will be emerging from their winter hideaways soon, so you might see one basking on a sunny morning. 

 There is another reptile, living in the Burren, which looks like a snake – the slow worm; but it is a legless lizard, and was introduced sometime in the last century. 

 Amphibians are divided into three groups – salamanders and newts, frogs and toads, and caecilians (worm-like creatures found in the tropics). While they are not as feared as snakes, some people do find amphibians slightly malevolent – think of the witches in Macbeth stirring “swelt’red venom” of toad, “eye of newt and toe of frog” in their bubbling cauldron. Many amphibians do have toxins in their skins, and bright warning colours for deterring predators, but they won’t harm humans, unless we eat them: the rough-skinned newt from North America, for example, contains tetrodotoxin – the same toxin found in puffer fish (fugu in Japan, which, if improperly prepared, can prove lethal). 

 Other notably toxic amphibians are the poison dart frogs from South America, used by indigenous hunters to poison the tips of their arrows; the cane toad, introduced into Australia to eat insect pests, which instead is poisoning the native marsupials; and the Colorado river toad, whose skin secretions can produce psychedelic effects, like magic mushrooms.

 Most salamanders and newts are small, though the gravely endangered Chinese giant salamander can grow to over one and a half metres. Our only species, the smooth newt, spends much of the year on land, hiding under logs or stones. It might be mistaken for a lizard, but its skin is smooth, not scaly, and like all amphibians, it lays its eggs in water. In the breeding season, the males of our lizard and newt species both have bright orange undersides, but the newt also has large black spots and a crest along his back and tail. 

 There are about 7,600 species of frogs, some of which are called toads; true toads are just members of one frog family. In Europe, frogs have smooth skin and hop, toads have knobbly skin and walk, but in the tropics they come in a huge variety of shapes, sizes and lifestyles. 

 The common frog is found throughout Ireland, and should be familiar to everyone. The natterjack toad, further distinguished from the frog by the green stripe on its back and the parotid glands (which contain defensive toxins), is plentiful in Europe, but here is found only in parts of Kerry and some other sites where it has been introduced. 

 There is much debate about how our amphibians got here. Some might have survived the Ice Age, living in almost ice-free refugia to the south (frogs can be very tolerant of the cold – the North American wood frog for example, freezes totally every winter – blood, organs and all). They might have travelled here by land bridges. Perhaps they are not native at all. Aodh MacAingill (admittedly not a zoologist – he was briefly Archbishop of Armagh) wrote in 1618 of these “very ugly creatures that are not found in our land through the graces of Patrick, our patron.” It has been suggested that the natterjack, anyway, was introduced.

 Whatever about the past, their future does not look good. A third of frog species are endangered; 120 have become extinct in the last forty years. Because they breathe through their skin as well as their lungs, and need both terrestrial and aquatic habitats, frogs are very sensitive to pollution, climate change and habitat loss. A type of fungus has badly affected hundreds of species; thousands get squashed on roads; and in many countries, frogs are part of the human diet. 

 One way to help frogs is to build a pond. It need not be anything fancy. When I lived in Zambia, a guttural toad waddled across my veranda most evenings, so I dug a small hole in the garden, big enough for a washing basin containing a few rocks and weeds. Soon, a fat female toad had moved in. Sadly, one morning, I found just her head and back remaining, sure signs of a mongoose – they know the position of a toad’s toxic glands. But we don’t have mongooses in Ireland, so stop all that mowing, strimming and poisoning, let part of your green desert go wild, and make a pond. A frog will find it; you might be lucky and get some newts too. 

Dr Jeremy A. Dorman

Dr Dorman is a zoologist and teacher living in West Cork.

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