Swirling swarms, virgin queens and carrier ants

In all that heat last month, and near enough to the silly season, these islands conjured not a single insect “plague”. No kamikaze squadrons of water beetles hammered the bonnets of shiny cars, mistaking them for ponds. No clouds of migrant ladybirds sent bathers shrieking from the beaches. No hordes of wasps pursued lickers of ice creams as they fled from St Stephen’s Green. (Indeed, where are the wasps? I haven’t seen one for weeks.)

For a really significant Irish insect plague, indeed, one could go back to 1688, when millions of cockchafers – "maybugs" – arrived on the coast of Connemara, borne, most improbably, on a southwest wind. Their locust-like progress inland, as far as Headford, was recorded by Dr Thomas Molyneux, one of the most active and observant Irish naturalists of his day.

“A short while after their coming,” he wrote, “they had so entirely eat up and destroy’d all the leaves of the trees for some miles round about, that the whole country, tho’ it was in the middle of summer, was left as bare and naked as if it had been in the depths of winter [and] the grinding of the leaves in the mouths of this multitude all together, made a sound very much resembling the sawing of timber . . .”

In due course, their “spawn” became fat white grubs underground, devouring the roots of corn, so that “the poorer sort of the native Irish (the country then labouring under a scarcity of provision) had a way of dressing them and lived upon them as food.” This could interest the current advocates of mass insect consumption, if already echoed in the historical diet of Australian Aborigines.

The spectacular migration of cockchafers, as Molyneux guessed, originated in France and stemmed from their own search for food. An abundance of food, on the other hand, can produce a population explosion. In 2009, millions of painted lady butterflies arrived in Britain and Ireland – "snowing" butterflies in parts of this island. The original source was the Atlas mountains of Morocco, where the wettest winter in decades had produced a forest of thistles, the food plant of the butterfly. The extra thousands of pupae launched the first northward pulse of this continuously-breeding species.


Ecstatic swirling
In Ireland, a totally natural and regular mechanism produces an annual swarming of ants in the sky, a phenomenon celebrated over Dublin in high, ecstatic swirlings of the city's swifts, starling and gulls, feasting as they fly. It occurs over several afternoons about now; may, indeed, already have happened, if humidity, windspeed and temperature were right. It is triggered by an astonishing synchrony of body-clocks in millions of ants in thousands of separate colonies.

A colony grows from the eggs laid by a mated queen. These hatch initially into workers, whose job is to forage and feed more larvae. As the colony matures in size, it prepares to reproduce itself by producing winged ants, both males and virgin queens.

The synchronised swarming of the nuptial flights brings together young virgin queens and males from miles away, thus refreshing the species’ genes. The swarms are also big enough to tilt the odds against any individual queen being eaten by a bird. The males are dead within hours, but the queens, often mating several times with different partners, spin back to earth and cut off their wings. They are ready to start a new colony.


Country and city ants
In Dublin's city parks and under sun-warmed garden paths of the suburbs, the black ant is generally the common one, while in the countryside it is mostly the yellow meadow ant that rises from the fields. Back in the 1930s, the naturalist Robert Lloyd Praeger encountered their swarms as he walked into Blessington, Co Wicklow.

"They became more abundant on nearing the village," he wrote (in A Populous Solitude, published in 1941), " and I roughly estimated that on the last half-mile of road over a million-and-a-half of ants were crawling, while in the air above the road they were so abundant that my clothes were quite brown with them.

“The fields on each side were thick with them, the windows of the hotel were alive with them, and my tea was richly flavoured with them. Unless they were confined to a narrow line down which I had the fortune to walk, there must have been hundreds of millions of them within a mile of Blessington.”

Around the village today, such a density of colonies is found only in the last few vestiges of old and permanent grassland. Here, left undisturbed, yellow ants carry particles of soil to build their small, free-draining mounds, angled to the warmth of the sun.

Most Irish farmland is now a quilt of intensive silage fields, ploughed and reseeded with rye-grass and compacted by machinery – no landscape for the industry of Lasius flavus or its annual flights of sacrificial bliss.

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