Little moth loves nuclear monster: There is one last colony of Sussex Emeralds, and it is in the strangest place. Nicholas Roe reports

MARK PARSONS and Peter Kirby are sitting in a bird-watchers' cottage in the middle of the shingle at Dungeness in Kent, holding down a moth. Outside, the nuclear power station stands starkly, emitting wisps of steam and the occasional human being. Mr Parsons is trying to mark the moth so that he can release it and see how far it gets in the wild. They pin it to a coffee table with some netting, he takes a felt-tipped pen and bends over one trembling wing. 'The ink's run,' he wails. Then he laughs, and so does Mr Kirby. The two entomologists box up the insect with the go-faster stripe, and reach for another one.

You have to forgive these men the odd slip. In their thirties, cheerful, boyish, they have been awake since 4am, gathering moths among the stones beyond the cottage window.

It is late, and the only food they have eaten all day is toast and jam. They were working late last night, too, setting insect traps in one of Britain's strangest ecological quests. They are here to study and save a tiny, beautiful creature called the Sussex Emerald moth, which has just one known breeding colony in the country - inside the perimeter fencing of Dungeness A and B nuclear power stations. 'It is,' says Mr Kirby, putting aside his boxes and walking into the sunshine, 'a perverse creature.'

Dungeness shingle is unique in Europe, five kilometres of pebble-dash landscape stretching inland from the sea's edge. Huts and occasional houses mark the horizon. The film director Derek Jarman has a famous driftwood garden here, and countless species of birds and insects thrive amid the windy emptiness.

The Sussex Emerald doesn't like any of that. It prefers to lay its eggs beside the power plants, where the ground is churned up by industrial activity. Nobody knows why the Sussex Emerald calls this home - that is partly what Mr Parsons, a scientific officer with the Joint Nature Conservation Committee, and Mr Kirby, an independent consultant, are trying to find out. They are also desperately exploring ways of spreading the colony elsewhere before some stroke of development or bad weather destroys it.

They load their car with boxes containing 19 inky-winged moths, and drive off towards the power station. They stop to let the moths go exactly where they were caught - a wave of the hand, and another temporary captive flutters to the ground to merge with the weeds and wild flowers. Tonight they will set more traps and see how many of their victims have previously been marked - then they will know how far a Sussex Emerald likes to fly and add another piece to the sparse jigsaw of knowledge surrounding the insect.

Mr Parsons and Mr Kirby have been coming here for three years now, on and off. It costs pounds 12,000 a year and up to 35 working days annually to do so, but they love it: a bit of research, a bit of scrabbling around in the stones, a pub meal, a cat-nap in the afternoon before the night unfolds around the glowing light-traps, all in the name of ecological diversity.

There are 2,250 types of moth in Britain, but few studies of individual species have been made. This work is special - but here is the irony: the Sussex Emerald attracts funding not simply because it is rare, but because it has made the perfect choice of a place to settle.

The nuclear industry is anxious to appear environmentally aware, not just for old reasons like Chernobyl and Three Mile Island, but because it faces a national review at the end of this year, a prospect which adds a certain fragility to its own future. An endangered moth seeking shelter in the shadow of a Magnox plant is a powerful promotional tool if you want to look green and clean, so the company picks up most of the research bill - and uses pictures of the Sussex Emerald in its brochures.

But these are cynical details. The important thing is a creature whose vulnerability became clear in 1991, when these two men were asked to carry out a survey throughout Dungeness to find out how the moth was faring at its only known site.

They got down on their knees and started counting caterpillars. They found just 88, all within the power station fencing. It was so tiny a figure that a single storm or a bit of building work could have exterminated the species. Plans were laid to establish colonies elsewhere, and the following year they came back for another survey. And that was when the real face of conservation work showed itself.

It was not grand or glamorous: two guys crawling around on the shingle, trying to spot inch-long caterpillars and photograph each micro-habitat. They found 500. 'My back hasn't recovered,' says Mr Kirby. This year they logged 1,400, so the trend is upwards - but unreliably so, because nobody has yet found another spot like Dungeness power station where the moths stand a chance of surviving.

They have studied 12 areas, including sites as far away as Hampshire, but the combination of the right vegetation and stony, partly-disturbed ground is not there.

Humans have created an environment for the Sussex Emerald, but cannot find its equal in nature. They cannot even guarantee the long-term future of the site that the moth calls home, partly because nobody really understands what keeps it there, but also because the 28-year-old Magnox plant must itself have a limited life.

The fight to save the Sussex Emerald may not succeed, which would be a shame, but it does provoke several trains of thought: about attitudes to nuclear power; about the manipulation of public affections; about our readiness to drop everything and help an obscure species of tiny moths.

'Some people say the condor is rare,' says Mr Kirby. 'But here we have something an inch across, and all on one site. It would not take much to wipe out a thing like that.'

(Photographs omitted)