Green-leaved buckthorn
A brimstone butterfly on greenleaved

It is such an exciting time. Gardens in Britain have never looked better than in this wonderfully retarded year. The roses have been out with the wisteria and the peonies have been pausing wondrously in bud. I marvel at it all about six times a day but I have been marvelling most at a little miracle …I am smiling at all-comers. It is amazing news. I am about to have butterflies.

The back-story begins in the week of Easter 2012 when all my academic colleagues disappeared. Only those of us with multiple Easter deadlines from the FT are still lurking in the ivory towers and needing a dinner to keep us to our work. In 2012 I was joined by a temporary migrant, Jeremy Thomas, Oxford’s distinguished professor of ecology. Together we sat down, classicist and entomologist, to a sort of Dinner with the FT, a cold chicken salad, hard-boiled eggs and more lettuce than I would have liked. Naturally there was a bottle of red wine, a Santenay Comme Premier Cru 2005, although I forget the price. Conversation turned to the college garden. Could we do more to attract butterflies without turning it into a tangle of nettles?

Thomas is no mean expert. He is the man who has recently reintroduced the vanished large blue butterfly to England and, amazingly, persuaded it to colonise an adapted bit of Somerset. After half a bottle of Santenay, he is twice that man. He described to me the sky-high migrations of the Painted Lady. He told me how to attract the Orange Tip. Then he came up with a plan of genius. If we could plant some green-leaved buckthorn, we would fill the college with brimstones, flitting happily on their lime-yellow wings.

In the Bible, brimstone appears famously in a punitive hail on the city after the men of Sodom in a fit of lust have tried to have sex with a visiting angel. You may like the idea of brimstones raining on academic life but personally I was captivated by the professor’s emboldened vision. Female brimstones, he told me, would be diving down from the sky to lay eggs on our buckthorn’s green shoots. Within weeks they will give the college a brimstone colony. There was talk of hundreds of brimstones from thousands of feet, scanning the world for buckthorn and descending on our little patch. By then the wine was finished and dinner for two was over.

Within a week a bundle of rooted stems of buckthorn duly arrived, delivered in a professorial plastic bag. Rhamnus cathartica is the correct variety, so I planted it loyally by a remote garden tap, just below the window behind which pupils, studying law, have been taught for centuries the mysteries of English tort. When lined out, the buckthorn, 2ft high, looked puny.

The leaves appeared but by June 2012 there was not a sign of a brimstone. They then attracted one female butterfly but emphatically not of the brimstone type. She was an elegant lady in shorts reading for a degree in medical science. I caught her by the garden tap, stealing leaves off the buckthorn on a sunny evening. “I only want a few herbs for the cooking,” she apologised, and when I told her that buckthorn was tasteless, she cheered up and asked, “Can I smoke it?”

If she did, the summer weeks rolled by in a parallel haze and there was still not a brimstone butterfly in sight. Excuses began to appear, a “very bad year for butterflies all round”, “technical factors”, and, perhaps even, “wasps”. Autumn came and all self-respecting brimstones withdrew to hibernate. The score on our buckthorn was precisely zero.

I admit to an unworthy inner gloat about “science”. Was he really a professor and would he ever stand the pace if he had to study ancient Greek? This year began no more promisingly, no brimstones, not even a visiting female and only a ruff of green leaves on our bait.

Then, miraculously, it changed. In this early June, Thomas was adamant. The bushes had “over a hundred eggs” and brimstones were certainly in business. Try as I did, I could not see any, apart from a few orange dots that turned out to be spots of rust. It was time for another dinner.

A fortnight ago we had one with a far better menu, lamb cooked to pink perfection and a bottle of Château Meyney 2004. Over it, Thomas taught me the brimstone’s habits, assuring me he had not hallucinated about those eggs. Its habits could hardly be more apt for modern Oxford life.

From a height of about 200ft, fertilised females have somehow scented our little patch of buckthorn, among the competing fumes of Oxford and what TS Eliot calls the light “on sweaty faces”, the sportsmen of our adjacent college, St Edmund Hall. They have dived down, laid an average of 50 eggs each on our leaves and scooted off. Thomas thinks we have attracted at least four pregnant females. Did they reproduce by virgin birth, I asked, like greenflies, or had our visiting ladies had sex?

Indeed, they had. In winter, brimstones hibernate in walls behind cosy coverings like ivy. In spring the males go on sentry duty “looking for pussy willow”, in Thomas’s words. The females then come out into the sunshine and the males perform an airborne dance in groups of five or more. The female checks them out and coolly rejects the advances of nine out of ten males. She is the very emblem of the New College undergraduette. She picks one, mates with him and gets what experts describe as a “nuptial gift”. These gifts used to be left on brides’ pillows by entranced husbands on the morning after their first night in bed. In the Middle Ages a besotted husband even left the title deeds to half of what is now Wiltshire, causing a monumental family lawsuit for centuries and the rest of us to wonder what exactly she had done the night before. Brimstone ladies do not get Wiltshire. They get a bag of food from their male’s innards, wrapped in a separate sack, rather like the wrapped bedtime chocolates which were in fashion with last year’s undergraduates. Does she enjoy it, I ask the expert? “So far as we can tell, yes,” is the answer, “very much”, but perhaps not so much as a fruit-fly’s compelling lust. Unlike her human counterparts she never takes a morning-after pill.

As dusk fell, the wine ran out and in academic gowns we went on a field trip, down to the college tap. Not a single brimstone egg was visible. There were black ants, greenflies and yet more rust. Had it all been the mirage of a desperate man? There was apologetic talk of a “recent hatch” or the “early chrysalis stage”. Brilliantly, Thomas then saw the evidence, some stock-still caterpillars, stretched like green pencils against the buckthorn’s nibbled leaves. My heavens, he is right. Some picky ladies have seen our bushes from among the clouds, honed down from on high and left their fertilised eggs. I am in shock, wonder and awe. In six weeks a brimstone-cloud will arise in college. Right now, I am busily preparing its nursery. The mothers have flitted off with about as much interest in their children-to-be as an Edwardian grande dame with a nanny. It is I who am buying them nutritious verbena plants, I who am putting down ant-killer with the eloquent name of “Nippon”. Trust the great professor and his Rhamnus cathartica and watch this column in August when his butterflies should be swarming. He is guaranteeing that they will not be plain old Cabbage Whites …

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