Little sand-bowl arrow snail at the point of no return Eye On Nature

ANOTHER LIFE:AS THE YEAR turns, we have to wait for the sun. The mountain looms in its way, so it's well past nine when, as if focused by the fiord beyond, a fierce beam reaches out to gild the islands, one by one, then the edge of the strand, then the spiky fringe of the dunes. Another hour and we're released from Mweelrea's shadow.

Such a crystalline morning took me down to the sands. The softest fall of wavelets underlined a stillness remarked by passing ravens.

They flew above a shoreline ravaged by the autumn clash of swollen river and tide, a maelstrom that swirled around the rocks meant to armour the edge of the fields. Mossy hollows of the dunes still held big, deep ponds, silkily glazed with ice.

The dunes are new, historically, together with their great lawn of machair. A map from 1838 shows the stub of sandhills from which they grew. At the seaward side they are rawly cliffed by storm-driven waves and within this century they could be gone altogether, the sea reaching in to swallow the lakes behind them.

Even on a beautiful morning, the human rift with nature crouches at the back of the mind. On a bare and battered strand, December’s gentler waves had left crescents of seashells, their bright mosaic crunching underfoot. A thousand limpets at a glance, no two of them the same; myriad bivalves at every scale; snails, clams, pieces of urchin in every colour. I sifted out the usual few to lose in the corners of my pockets –­ scallop shells the size of fingernails, rosy, orangy, stripy red; one beautifully black.

All the shells had one thing in common: they were built of calcium carbonate drawn from an alkaline ocean. But the pH index of the surface water continues to fall, as the sea absorbs more and more man-made CO2. Below pH 7 comes acidification. It threatens an unimaginable dissolution of species, not only shellfish, but crustacea, corals, plankton and other vital organisms. This was one of the spectres haunting Copenhagen.

Calcium from the ocean is also, as it happens, key to what is special about the whole ecosystem of Dooaghtry – as the tangle of maritime wilderness below me has been known to generations of ecologists. Powdered into sand from empty seashells and blown inshore across the dunes, the mineral is recycled into land snails of great, sometimes rare, diversity.

The new National Biodiversity Data Centre has been taken aback to find the size of Ireland’s share of the world’s non-marine mollusc species: they thrive in our moist, mild climate. And the four square kilometres of Dooaghtry are a remarkable land of snails, among the richest in Europe. Seventy species have been recorded here, from the big “garden” snails, sandblasted blue in their winter niches in the rocks, to creatures no bigger than a match-head and invisible in mosses at the edge of the lakes.

Rarest of all is a snail with a shell that at least you can see, almost a centimetre long. And for once, in the heady mix of Latin that bedevils snail appreciation (think of the threatened Vertigo geyerithat attracted Bertie Ahern's derision), it has a decent, even cosy, common name — the sand-bowl amber snail.

Its latest scientific appellation is Quickella arenaria, immortalising the English ophthalmic surgeon and malacologist, Hamilton Quick, who discovered it in 1933. This entailed fine dissection to discover, among other idiosyncrasies, an arrow-mark at the end of its penis. That helps to mark it out from the rest of the Succineidae, a wetland family with variable but closely similar shells.

My drawing is made from a photograph taken on a mossy flush at Dooaghtry, on a warm and very wet day last summer. It was taken by Dr Evelyn Moorkens, the scientist to whom we owe such trenchant defence of the few freshwater pearl mussels struggling to survive in our rivers. Prostrate on the moss, with a hand-lens, she found the pictured snail on butterwort leaves, with Vertigo geyericloseby. Quickella, she told me happily, was "having a terrific reproductive year".

The snail has been lost from its other three Irish sites, in Offaly and Tipperary, where drainage destroyed its lime-rich habitats at the edges of raised bogs. Dooaghtry is possibly its most important site in the world and a Special Area of Conservation. But the snail’s reliance on wet mossy flushes, many less than one metre square, make the hooves of sheep and the random passage of four-wheel drive vehicles formidable threats to its Lilliput world.

This is the UN’s International Year of Biodiversity, and either we care about losing the world’s species, however uncharismatic, or we don’t. Among them, you know now about the sand bowl amber snail, a tiny hermaphrodite gastropod with an arrow tattooed on its willy.

The Horizons column will return next week

Eye on Nature

On a visit to Vienna I noticed the leaves of the horse chestnut were wilting far too early, and was told that this was caused by the caterpillar of an unidentified moth. Could you help with the identification?

David Power, Drimnagh, Dublin 12

It is the caterpillar of the mothCameraria ohridella , also called the horse chestnut leaf miner. It is a tiny moth, only 5mm long, and the caterpillar is about 1mm. They mine inside the leaf under the epidermis leaving pale blotches which later turn brown. It has spread westwards across Europe from Macedonia in less than 10 years. Although found in Britain I have not heard any reports of it in Ireland.

Recently a little red squirrel came into the back garden and right up the back of the house to a first-floor windowsill where I sometimes feed the cats when there are dogs around.

Georgina Campbell, Howth, Co Dublin

I’m confounded about a grouse I saw wandering the length of my garden recently. I live near the Phoenix Park, and I wonder could it have wandered out from there or from the Zoo.

Ann Hearne, Dublin, 7

It was much more likely a female pheasant.

• Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo. Email : viney@anu.ie. Please include a postal address.