Beetle mania

I am beginning to think something may have befallen Megabyte, my weevil friend, more formally Otiorhynchus clavipes, he-of-the-big-nose-shaped-like-a-key. Nearly every spring for a decade, he (or a successor) has appeared on my desk on a warm morning around Easter, tracking six little ink-blot feet past the paper-clip bowl and ducking under the mouse cable on his way to - wherever it is he goes.

Ageing fans of the 1920s Don Marquis stories about archy and mehitabel (archy was a cockroach hopelessly in love with the office cat) will expect me to quote poems that Megabyte has written on the computer overnight, all in lower-case letters. But if a cockroach couldn't manage the capitals key on a typewriter, what chance has a weevil of booting up a Mac?

No, Megabyte's job is to help to underwrite the spring - and I can only hope I haven't accidentally flattened him with a mug of coffee or the Oxford Dictionary of Natural History. More likely, he has run into a dearga daoil at carpet level, for the devil's coach horse, biggest of our rove beetles and a deadly stalker of weevils, insists on the run of the house.

With or without Megabyte, spring arrived on time and with an extra flourish: never such a brassy blaze of celandines in the Hollow; never so many self-sown primroses scenting every scrap of shade. Bumble-bees are nuzzling the catkins at the highest twigs of the willows. And we have even had the first newspaper story about an insect plague in England. "Hungry beetle on rampage" turns out to be a fairly rare wood-boring longhorn which, in Ireland, is unlikely to survive at all out-of-doors.

With global warming no longer a matter for argument, we are due both a long, hot summer and an accompaniment of tabloid "plagues" on the island next door. You may remember 1976, when billions of ladybirds descended on coastal resorts in south-east England and drove holidaymakers from the beaches amid reports of people being "bitten" or "stung" by the bright little beetles.

It happened when a mild winter and wet spring produced a lush growth of crops and cereals which led to a population explosion, first of aphids and then of the ladybirds which eat them. When the aphids were all gone and the host plants withered in the heatwaves, the ladybirds searched for food further and further afield until they reached the shore, where even human skin seemed worth a nibble.

Such eruptions are scarcely new. One of the earliest "plagues" described in Irish natural history was a series of mass migrations of cockchafer beetles in the decade from 1688. They arrived in Connacht on warm winds from Spain and flew about "with a strange humming noise, much like the beating of drums at some distance, and in such vast incredible numbers that they darkened the air for a space of two or three miles square." To find beetles behaving like migrant butterflies seems extraordinary: even more odd is that this has never been repeated - at least not when a naturalist was looking. But more insects make long-distance movements than one might think. In July, 1995, two Irish biologists in a boat off the Cork coast watched long skeins of hoverflies - bright, benign jewels of our summer gardens - flying in from the sea in company with red admirals arriving from Europe.

Hot summers and southerly winds could, indeed, bring us pleasant visitations - colourful hordes of painted ladies and clouded yellows, even American monarch butterflies (already resident in Spain and Portugal). But, as we saw last year, a rise in global temperature is not at all inconsistent with a miserable Irish summer, and the west of this island could be sentenced to long and muggy, Labradorian glooms while south-eastern England simmers in perennial droughts.

Even without aerial armadas from the south, pleasant or otherwise, global warming could bring about big changes in our insect populations. On my own acre, several young Sitkas are looking distinctly brown and threadbare - attacked, I suspect, by the green spruce aphid, which makes the young trees lose their needles. Milder winters have already brought an upsurge in aphids of this kind. Summer droughts, on the other hand, can make trees and other plants lower their chemical defences against insect attack. Just one degree rise in temperature is roughly equivalent to a southwards move of 200 km, and even a spread in the natural ranges of insect species within these islands could bring unfamiliar creatures into our countryside. The warm south of England is rich in species which have rarely been seen further north - grasshoppers, crickets, butterflies, dragonflies and wasps are just some of them. But a species bonded to a special habitat (chalk grassland, for example) or a particular foodplant, will not expand by temperature alone, or take long leaps across inhospitable territory.

Ireland, so much smaller and more homogenous, has far less room for change of this sort, but the natural barrier of the Irish Sea - indeed, of all seas - is being steadily subverted by road haulage, tourist ferries and aircraft, and the trade in fruit and garden plants. Warming will increase the chances of immigrant species surviving - such as undesirable alien mosquitoes, to add to the 18 species we have already.

Some of our more welcome regular migrants, on the other hand, may be induced to take up residence. In Ireland and Britain there are increasing records of hibernating red admirals, and now even one of a painted lady, from North Africa, surviving the winter in Cornwall. In the UK's Butterfly Conservation News, a professor tells how he marked the butterfly in October, 1997 with a bright green dot on its wing and found it again, perched at the same warm spot on his gravel drive, in early April.

Anyone with a knowledge of butterflies can help this summer in the first major Irish survey, launched by the Dublin Naturalists' Field Club with funds from the Heritage Council. This ties in, first of all, to the Millennium Atlas project of the UK's Butterfly Conservation charity, but will also create a badly-needed national network of volunteer observers. For details and record cards, send a large SAE to Mary Willis, 18 Charleville Road, Rathmines, Dublin 6.