Too much temptation for sun-loving insects

Another Life: On my knees in the polytunnel the other afternoon, I was counting my considerable blessings. The tunnel has, for one thing, a splendid acoustic: a clarinet quintet from Lyric chimed nicely with the birdsong beyond the open doors.

The breeze they ushered in and out was in perfect balance with the tunnel's fierce lens of sunlight. One door framed boughs of apple blossom against the mountain and a wedge of blue sky, the other a hawthorn hedge in pearly bud. Bumblebees drifted through, drawn to the scented, crimson flowers of a "very rare" broad bean (rescued in 1978, swears the Irish Seed Savers' catalogue, when 73-year-old Rhoda Cutbush passed on her four remaining seeds: how could one resist?).

But also, I was thinking, as I used a bare hand to scoop out holes for sweet-corn seedlings, how lucky we are in Ireland not to have really toxic wildlife: no asps, funnel-web spiders, poisonous centipedes, hornets or fire ants. If not at that precise moment, then within its narrative proximity, I was well and truly stung on the side of the neck.

As I swiped at my collar and swore and swiped again, a second bite burned into my skin. Since nothing had buzzed, and the silent, blood-sucking clegs aren't around until late June, it had to be ants. For the first time in my gardening life, they had started to strike back, and with something more aggressive than a squirt of formic acid, such as the yellow meadow ant might give.

It has always dismayed me to shatter an ants' nest with an accidental stroke of fork or spade and watch, as if from the sky over Guernica, the panic of the populace, snatching up their children and running for the cellars. Unfortunately, the raised soil beds of the tunnel, with their walls of decaying logs, are all-too-tempting to sun-loving insects in search of free district heating and good drainage. I hadn't broken into any nests on this particular afternoon, but no doubt there were old scores to settle.

Dabbing anti-histamine cream on big red swellings that took half-a-day to subside, I consulted books and the internet to identify my assailant. On my knees again with a magnifying-glass, I found a tiny wanderer at the scene of the crime: dark, rufous-red, double-jointed waist - probably Myrmica ruginodis, one of the red ant Myrmica tribe that has kept the capacity to sting (in Australia they jump at you as well) and a notable nester in rotting wood.

Ireland's uncertain sunshine has helped to limit our share of ants - a mere 18 species compared with Britain's 50 - and much remains to be done about knowing where they are. Last summer, Dr John Breen of the University of Limerick roamed the Burren with a knapsack full of breadcrumbs. He scattered them carefully at five different locations, each measuring 10 metres square, and then looked at what turned up - or didn't - in each of the 500 one-metre squares, or "quadrats" within. At least one species appeared in all but 69 of the squares, and totalled 13 kinds of ant, which makes the Burren, yet again, a national oasis of biodiversity.

One of them, Formica lemani, is a black ant especially happy under the warmth of limestone, where it often shares its nest with an unscrupulous lodger, a rare hoverfly called Microdon mutabilis. By mimicking the appearance of its hosts, the fly is able to lay its own young in the nest, which then feed on the brood of the ants.

Another of the Burren species, Myrmica sabuleti, is now specially well-known to naturalists for an even more remarkable relationship, with the caterpillars of one of Britain's rarest butterflies, the large blue. This lays its eggs on the flowers of wild thyme growing on warm, sunny, short-turfed banks where M. sabuleti makes its underground nests. When the hatched-out caterpillars are still tiny, they drop to the ground and attract the ants by exuding a sort of honeydew (like aphids). They then hunch up to mimic ant grubs, whereupon they are carried down into the ants' brood chamber. Here they feed on the ant grubs, pupate underground, and then, upon emerging as adults, crawl back up into the sun to spread their wings and fly.

This extraordinary parasitism on a single ant species, needed just the same closely-grazed habitat as the caterpillars' foodplant. When the habitat disappeared, the large blue became extinct in Britain in 1979. Understanding these links has now guided restoration of sites for the butterfly in North Cornwall for its reintroduction from Europe.

The large blue, a sedentary species, never reached Ireland. But it was worth getting stung to be reminded how natural selection can spin such improbable connections.