Take On Nature: So just how did frogs come to be in Ireland?

A common frog, rana temporaria, pictured in Co Meath
A common frog, rana temporaria, pictured in Co Meath A common frog, rana temporaria, pictured in Co Meath

SOME weeks ago I came upon the unpleasant sight of the flattened remains of a common frog, rana temporaria, obviously a traffic casualty as it attempted a road crossing on its migration to some nearby breeding site.

Having emerged from hibernation, male frogs congregate in large numbers at watery spawning ponds before striking up a chorus of loud croaking to attract females. In a strange way, the squashed amphibian was a symbol of hope as it heralded the coming of spring and the promise of new cycles of life.

The origin of the frog in Ireland is controversial and uncertain. Many early writers and naturalists believed they were not native but that they arrived here accidentally or by deliberate introduction. Donatus, (Donnchad) an Irish teacher and priest who went on to become bishop of the Italian town Fiesole, near Florence, wrote a poem in the ninth century about his memories of Ireland and referenced the absence of frogs here in that "Isle of ancient fame," where "No poison there infects, no scaly snake / Creeps through the grass, nor frog annoys the lake."

The earliest reference to frogs in Ireland comes from Gerard of Wales who writes about their appearance in Waterford, possibly from a passing ship, after the arrival of the Normans in the 12th century. Other sources suggest they were introduced here in early 1600 by students of Trinity College who brought them from England, while another account written by the Rev John Dubourdieu, rector of Annahilt, in the 1802 Statistical survey of the Co Down states that frogs were first seen in Ireland in Moira, Co Down in the 1750s and from there, "spread throughout the country".

More recent genetic studies (Teacher et al, 2009) indicate, however, that our common frog may have colonised Ireland in the early postglacial period from a glacial refuge population in the south west of the island, meaning that it is in fact a longstanding native.

Whatever the origin of the common frog in Ireland, it is now widespread throughout the country, using wetlands, ponds, streams and ditches as spawning grounds and the surrounding long rough grass and scrub cover for terrestrial foraging. During spawning the female can lay up to 2,000 eggs which are fertilised immediately before their jelly capsules absorb water, swell and rise to the surface.

Nobel Laureate, the late Seamus Heaney describes this frogspawn from childhood memories in school in his poem Death of a Naturalist, writing of "the warm thick slobber / Of frogspawn that grew like clotted water / In the shade of the banks". He goes on to reminisce on how, "The fattening dots burst into nimble / Swimming tadpoles.’’

After fourteen weeks feeding on algae and aquatic insects, they become tiny froglets and vulnerable to their predatory enemies the fox, otter or heron. Feeding on slugs and worms, those frogs which make it to winter will hide under tree stumps or rock piles, entering a state of torpor until the following spring.

Frogs feature in much Irish folklore often viewed as creatures of the underworld associated with witches and to be used in the preparation of potions and spells. Putting a frog into the mouth of a child with the whooping cough three times and letting it swim off in water was said to cure the child. A live frog in your mouth would also cure a toothache and a sore throat. Such folk cures may account for the saying, ‘I’ve got a frog in my throat’.

Last words to Heaney again: "You could tell the weather by frogs too / For they were yellow in the sun and brown / In rain."