Another Life: How much would you pay to save the hairy wood ant?

The question of what another of Earth's species is "good for", delivered with lifted eyebrow and sceptical jut of the chin, can open up a whole can of philosophical Lumbricidae . Good from what, or whose, point of view? After decades of green enlightenment, the range of popular insight into purely human benefits from nature has grown enormously. Earthworms tunnelling for agriculture, bees for pollinating fruit, deep-sea sponges offering tomorrow's cures for cancer – the wider sense of nature in humanity's service has never been keener.

Then there’s the heritage bit – saving birds and butterflies for our grandchildren to enjoy, or whales and dolphins that might boost the tourist trade. Even current human pleasure in nature can be given economic value by asking people how much extra tax they would be willing to pay to protect a threatened species, or enjoy a particular habitat. For example, Irish university researchers recently asked a 1,000-strong sample of people for their willingness-to-pay (WTP) value for public access to the nation’s forests. This “non-market value” of afforestation – conditional, as it proved, on proper regard for wildlife – surprisingly worked out at a respectable figure of up to €89.94 a year.

Charismatic species like pandas, elephants or tigers command ready respect and support, with no demands to know what they're "good for". But biodiversity conservation means looking out for species most people have never heard of or would want to find walking on their leg. What WTP, I wonder, would be offered towards conservation of Ireland's hairy wood ant, Formica lugubris , one of this island's rare and "near-threatened"creatures given special concern in the EU Habitats Directive?

A word on its edgily comical name . . . This centimetre-long insect has a sort of forelock of hairs, and distinctive red and black colouring that its discoverer, a Swedish naturalist called Johan Zetterstedt, appears to have found mournful when walking the dark Scandinavian woods in 1830. It is one of the wood ants still present in billions across the forests of northern Eurasia, from Ireland to Japan, but now threatened by human inroads into the trees. In Ireland the species is in serious decline, dwindling westwards to a main stronghold in Coillte woods in Co Tipperary, with more nests in Killarney National Park and Co Galway.

For decades its fortunes have been among the special interests of Prof John Breen, an entomologist now retired from the University of Limerick. His new dossier on the ant for the National Parks and Wildlife Service calls it "an iconic keystone woodland species" deserving special measures for conservation. It is certainly a most intriguing candidate for care.

For a start, it’s an ancient colonizer of Ireland, genetically distinct from the hairy ants of the island next door. They could have been blown in on the wind or floating on driftwood – or perhaps arriving on a very long march, with the post-glacial trees, from some conjectural offshore refuge to the south. And unlike its opposite numbers in Britain, it builds fewer nests per colony and raises only one queen in each – factors that now add to its vulnerability.

Unlike other European ants, it builds conspicuous mounds above the underground chambers of its nests, siting them on sunny spots along rides and in clearings, and sloping them southwards to catch the most warmth. It thatches the mounds with fallen pine needles lined downwards to carry off the rain. The nests also attract many insect “myrmecophiles” – species of beetles and spiders that contrive to lodge profitably with the ants without incurring their wrath, sometimes by mimicking their shape.

F. lugubris is otherwise an aggressive and dominant predator – Dr Breen's dossier has pictures of workers returning to the nest with sawfly caterpillars bigger than than themselves. Like most ant species, they get the bulk of their summer energy from sipping the excess of "honeydew" sugars sipped from the backsides of sap-sucking aphids – not just any sugars, so not just any aphids, but just the right chemical cocktail from species it approves of and protects from predators. These are the aphids of particular trees – in conifer forests, the Cinara aphids of Scots pine, Norway and Sitka spruce, and larches. In Killaney's native woods, it's honeydew from one aphid that feeds on oak shoots and another that sucks the juice of birch.

All this is certainly wondrous, and clearly important to the immediate ecosystem, if not, perhaps, immediately persuasive of what hairy wood ants are “good for”. This needs the ethical leap of faith that awards nature an inherent value, a scientific need or right for a species to exist – constructs increasingly borne out the more we learn about ecological balance. .

Meanwhile, looking after hairy wood ants means giving them enough sunshine in our forests, planting enough Scots pine, spruce and birch, in the right succession and places, and not driving machinery through the nests. But no lodgepole pine – it apparently doesn’t have aphids at all.