Adam ran his hand over his balding scalp. The dunes shimmered all around – expectant, empty of any movement except his, although he knew rare beetles trundled through rough grass, and he could hear toads, chirring contentedly somewhere amongst orchids and buckthorn. He couldn’t see the sea from here, but it would be far out at this time, perhaps exposing the ribs of the Sprite, which had foundered here fatally in 1888.

A track wended up a slope surmounted by wind-tortured hawthorns and a World War Two pillbox – an outsized armoured helm in lichened concrete. This had always been a watchful coast, wary of invaders or worried by water, fearing one day it might break through to complete the drowning of Doggerland. There were times – more and more often – when Adam remembered the world’s hugeness, and hardness. Its terrible hardness…

He sighed, and sweated up the slope. Bone-weary though he was, his eyes were darting everywhere. He had tofind it. Had to. It would be his first. It would be his last. It would crown the day, this year – in fact, his nature-watching life. And it would be the perfect sign-off for this place, which he’d soon be leaving for good.

Angela had loved it here. So many days here with her, sharing the exultance of seeing some creature that according to the textbooks shouldn’t be there at all, some visitant magically manifesting thousands of miles outside its accustomed range. Once, when lying beside her under bushes, watching a vagrant warbler almost never recorded outside Central America, she had breathed just audibly, “It’s like a miracle!”

So it was – although there was also sadness surrounding such wanderers, so far from home, never to return, fated to end among unfamiliar dangers, trembling in unaccustomed cold, calling out plaintively into unanswering air for flock or mate.

Birds had been Angela’s passion – house-sparrows as much as any exotic warblers. She had never taken any species for granted since reading as a girl about the passenger pigeon. They had even given their daughter the name of Martha, in honour of the elderly endling which had fallen to the floor in Cincinnati Zoo in 1914, the last representative of flocks which had once broken branches by sheer weight of superabundance. On that proud day at the font in sunlit St Michael’s, with smiling family all round, they had never considered their choice might be so portentous…

Adam was more interested in insects. They had fascinated him since he was four, after a hoverfly had alighted on his outstretched hand like a benediction, a gold-and-black bejewelled being gracing his hand in a God-ray of sunshine slanting through trees.

He had lived insects and arachnids since, keeping ants and stick-insects, rearing moths, watching Attenborough, reading books like The Life of the Spider and The Soul of the White Ant, habitually turning over stones and rotten logs – in incessant search of insect lives, their meanings, their secrets, their symbolism.

Medieval illuminators had made minibeasts into miniature marginalia, and philosophers had seen them as metaphors of society and statecraft. The bee-kings that became queens as science advanced – the toiling workers so infinitesimal in themselves, but whose united efforts brought strength and sweetness to the world. Adam owned a small 1660s still-life, an anniversary present from Angela – a Delft bowl of apples, grapes, pears, and pomegranates, festooned with delicate butterflies – a Golden Age representation of Earth’s bountiful interconnectedness. Insects intersected with everyone everywhere always; their fall would also be ours.

He had become an academic, a writer of papers and addresser of conferences, a campaigner and charity trustee – so often dull and dry work, filled with frustrations, but energised always by that childhood encounter, and then the prospect of the whole planet losing its pollinators – losing its life. Losing its soul.

Whenever things got bad, there was balm in the multi-legged multiverse that began outside his back door. He would switch off machines and go into the garden – there to lose himself in the polished elegance of earwigs, watch whirligigs writing in an unknown language across the pond, or look into the compound eyes of bee-flies and wish he could see the world their way. Invertebrates had more sense than some vertebrates. Their unflagging energy was humbling as well as inspiring, an example of courage to him and to everyone – how they would resurge after every reverse, like bees building each spring, or Robert the Bruce’s spider in the cave. Insects had seen dinosaurs pass; woodlice would probably see us out.

He interested himself intimately in insects’ activities, intervening like a god when provoked by some miniscule plight. Even today, with his mind filled with his quest, he stooped to move a burnet moth caterpillar from a bare sandy tract that from its perspective must have seemed miles wide, and placed it on the sappy stem of a ragwort. Caterpillars found out in the open were often dying, he knew, driven insane by parasites eating them inside. But maybe this one might just make it. And anyway, it was indecent to leave a helpless creature – just as sick people deserved treatment, at whatever cost, and however distant the chances of success. However futile, even – however blackly written in the book of mitochondrial heredity.

An emperor dragonfly angled electrically into view, and he watched it zigzag away like an escaped ampere – a spectacular insect, whose even larger ancestors once darted over drowned Doggerland. Land and sea so often seemed interchangeable along this littoral, confusing even the animals. He sometimes found insect-falls along the advancing edge of the sea – ants, devil’s coach-horses, ladybirds – tiny fragments of feeling kicking their legs helplessly or crawling desperately away from the water at the salt end of all things, pitifully paralleling the great human-falls of history. He always lofted as many as he could away to safety, although aware he was making little difference, and that all safety was at best a postponement. Under every summer beachscape lay freezing physical forces, under sun-warmed wavetops a constant churning of cold deeps, and under the fine sand sliding earth plates, all part of the constant longshore drift of life into detritus.

As Adam aged and ailed, some of his students joked that he looked like a late-summer lepidopteran. Mr Mothman, they called him – an upright and ugly imago. His skin grew dry, thin and chitinous, and his bones increasingly prominent, as if he was turning inside out, developing an exoskeleton. But why shouldn’t his softness hide inside? Life had so often shown him need of a carapace.

How he wished Angela could have been here today, of all days.

Late yesterday evening, when Adam had been reading a local nature blog, he briefly stopped breathing. Just a few casual words, written by a local nature-guide, mentioning that a Camberwell Beauty had been seen the previous day. It was the most wonderful of shocks. A Camberwell Beauty!

For much of his life, Nymphalis antiopa had been flitting through Adam’s imagination – an apparition flapping always in front, just out of reach. He couldn’t remember a time when he hadn’t known of the butterfly’s existence. But then his first home had been on Coldharbour Lane, where the butterfly was first recorded in 1748, by a man named Moses Harris, who called it ‘Grand Surprise’ to register his astonishment at its size and striking appearance – richly maroon wings, with blue dots and creamy yellow fringe, and powerful un-butterflyish flight.

It had stuck out even in Moses Harris’s still semi-rural, semi-magical London, with Camberwell still famous for fruit growing, and Peckham Rye nearby, where Blake would soon see angels in the elms. Science itself was still in a state of wide-eyed and wondering innocence, where each day brought discoveries which could still be attributed to God’s benevolent grace, and clustering new species were named after characters from Greek myth. There had been many Antiopes in Attica, but Adam was sure the Beauty must have been named after the daughter of Aeolus, or the consort of Helios, or maybe in honour of both, seeing that the creature was the most perfect union of air and light.

The boldness of the Beauty had clearly compelled Harris, who as well as being an entomologist, had also been an engraver and theorist of colour. Adam had sensed the other man’s aesthetic and aurelian excitement across the gulf of years – although for Adam excitement had always been mixed with melancholy, because the Beauty hadn’t been seen in Camberwell since the early twentieth century.

Others people had noticed, and mourned the butterfly’s absence. It had been referenced in literature and music, and there was a huge mosaic of one on a building in Burgess Park, moved there in 1982 from a demolished 1920s printworks, which had used the already rare butterfly as emblematic of their expertise. Adam remembered the mosaic in its prominent original location, and being told that the Luftwaffe had ironically used it as a navigation aid for raids.

But Adam felt the insect’s absence almost physically – felt it like a folk-memory of destroyed wildness, felt it like the pains amputees imagine in absent limbs. He almost envied the long-dead who had glimpsed the Beauty in habitats like those he had known – battening in Brixton back-gardens or fluttering up Forest Hill, or beating between the Hammer Horror monuments of Nunhead Cemetery, a Gothic shade among the white angels and the ivied urns – the Germans’ name Trauermantel (‘mourning cloak’) so suitable in that context, so redolent of the insect’s elusiveness, and adjacency to extinction.

Nymphalis was quite common elsewhere; Adam had even seen a subspecies in Sweden. But it was surrounded with special significance for him and all English lepidopterists, including the Edwardians who were the last to see it in London. Those Edwardians, with which Camberwell always seemed synonymous – those bicycle-clipped, moustached City clerks, with their copies of Illustrated London News, and Elgar on wax cylinders – so often seemed frozen in photos, fixed in period the way old collections of coleoptera were pinned to museum boards. But they had been wonderfully alive in at least one respect – to have had even an outside chance of seeing Beauties in their rose-gardens, flying in from some other realm to enrich their Arts and Crafts universe.

The Camberwell Adam had known as a child, then heard about as an adult – an anthill without purpose, a place of bad air, cars, crime, and riots – had seemed daily less likely to throw up Beauties. So now, one had kindly come to him, was waiting for him, possibly just over this hill – his personal ‘Grand Surprise’ sipping the sap of a willow, or winging royally across rabbit-nibbled clearings, the ultimate prize for hours of exertion on the hottest day of the year, the culmination of a life’s longing. This was circularity. It felt a little like – destiny.

How could it have come? Some came over the sea in some years, but very few, and never this far north. There were theories about pupae carried in cargoes of Scandinavian timber. There were also rare private rewilders, eccentrics or idealists who raised and released animals they felt ‘belonged’, animals which had a moral right to be in particular places. Aged eight, Adam had met one, the famous Leonard Newman, who had signed Adam’s copy of Complete British Butterflies in Colour – a book outdated even then, but still on Adam’s shelves. Newman had reared thousands of Beauties and let them fly in Kent one hopeful spring, then waited…and waited…and given up.

Adam knew why Newman had done this; skies that had known the Beauty must one day know it again. But he wanted to think this specimen had somehow made its own way here, acting on some unknown impulse, linking his early life with his late – bringing old London to modern Lincolnshire. It would be kismet – completion – closure.

He had sometimes worried that if he ever caught up with the Beauty it might feel like an anti-climax. Species ticked off lists were like sports trophies – wholly inadequate, tinny mementos of a very different day, a different outlook, whole other worlds of happiness and health. And this just wasn’t any species. The Beauty dwelled by itself. It had flown in front of him for so long that finding one might feel more like losing something. But if this was a risk, it was one he had to take. What else would he do? What else could he do? It was his nature. Angela would have understood – and Martha.

He fantasised hotly, the sun boiling the reddened skin of his scalp. There might be more than one. A venturesome individual might be the vanguard of a viable colony. Could this bold outrider be a scout – the crest of a climate-adapting wave, coping with change by expanding range? He knew, in truth, this was a fancy too far; the Beauty liked cooler climates. But somehow, somewhere among all this global destruction and private desolation, some species must find a way forward, lead a rebirth and recolouring of the cosmos. How wonderful it would be if at least a few beautiful things could defy the world’s contagion…Was that too much to ask? There was so much loss, so much waste and death…

He stopped to get breath, and looked up, to see the sun well on its way to the west. There weren’t many hours left. There were never enough. There was never enough time for anything. Angela and Jane were also now flying in front… He pushed on through trees and across a wide wasteland, while a large butterfly on the highest branch imperiously flared indigo wings, and indifferently watched him pass.