Red admirals swerving in scarlet spirals

 Another Life: A gleam of light over the mountain pierced a lowering sky and outside the window a small, dark flicker of response caught my eye, like an autumn leaf twirling upwards. Defying the next and imminent shower, a red admiral butterfly was reclaiming his airspace between the big willow and the house.

This has become an ideal territory for Vanessa atalanta - a small, south-facing, sheltered, bushy glade a few grassy metres across, with a wall to store up what little warmth there is. For years, now, a red admiral has taken up his watchful perch in August, as predictably as bluebottles on the blossoming angelica or migrating swallows on the wire above. This year the new tenant is early: no surprise, perhaps, when a (presumably) overwintering red admiral with tattered wings was spotted laying eggs on Howth Head nettles as early as March.

While he waits to intercept a passing female, the admiral will dash at almost any flying object of around its own size: even a queen bumble-bee may swerve from the assault. But when Vanessa herself comes by, the courtship dance is beautiful to watch: the insects spiralling up around each other in a sparkling weave of scarlet, white and black.

I would like, of course, to think that the same line of red admirals land on the site from year to year, like swallows returning to family nests in the woodshed. But there are too many generations of butterflies and there is too much chance at work to make such site fidelity at all probable, even in insects already given to the miracle of metamorphosis.

Keeping track of butterflies is hard, but people try. In the US this summer, a small army of "citizen scientists" recruited by the Entomological Society of America have been feeding in their sightings of red admirals to an interactive map of butterfly migration. But the Vanessa Project plots a mass movement northward, not any individual insects within it.

Butterflies have been marked with felt pens, or their caterpillars fed a dye that, eventually, stains the adult's eggs - this mainly in studies of local, resident populations. In experiments in Germany, peacock butterflies (the ones with big "eyes" on their wings) have been recovered more than 90km from the place where they were first caught and marked. But with such a large pool of red admirals breeding in Europe, and so many now deciding, in a warming Ireland and Britain, to stay put for the winter, speculation on this butterfly's travels is full of uncertainty.

More to the point just now is charting the distribution and status of our 28 resident butterflies, not just for their own sakes but as a collective barometer of what is happening to their respective and greatly varied natural habitats. The Dublin Naturalists' Field Club, with more than 100,000 records in its database, has made a good beginning (see www.butterflyireland.com) and has fed its records into the new National Biodiversity Data Centre, which is based on the campus of the Waterford Institute of Technology.

Now, the centre makes butterflies and moths the theme of its "First Annual Event for Recorders", in which amateur and professional naturalists, ecologists and conservation workers will spend two days (August 22nd and 23nd) comparing Irish and UK experience and learning to improve their skills at field identification and recording (not only of butterflies, but bumblebees and spiders as well). The centre's director, Liam Lysaght, has encouraged more than a dozen butterfly walks this summer, to test the prospects of establishing a national butterfly monitoring scheme next year.

As I write, at another window, a red admiral has just fluttered down from the sky, ducked in under the hedge and suspended itself from a leaf of escallonia, its cryptic underwings fading at once into the shadow. Another shower from the west spatters across the glass.

That's nothing. On June 10th, Derek Scott of Dursey Island in Co Cork recorded "a spectacular arrival of immigrant Lepidoptera including hundreds of red admirals, painted ladies and silver Ys along with at least one bedstraw hawk-moth and a hummingbird hawk-moth . . . Suddenly the garden was full of them, streaming from the south-west, stopping briefly to feed on the mass of flowers in our garden (especially the Hebe and campion) and then heading off north-east up the hill. Several hundred must have passed through in the space of an hour."

Details from mwalsh@biodiversityireland.ie