Nature Studies by Michael McCarthy: The dazzling wings that define summer

What is the supreme marker of high summer? What sensations most come to mind of hot, lazy days? Do you see a yellow beach, a blue pool, or hear the shouts of children splashing? Do you hear the purr of an evening lawnmower? Do you taste rosé wine, chill and savoury in its glass? Do you smell a barbecue aroma wafting across from a neighbouring garden?

All of those resonate with me, but they're based around human artefacts, whereas I think my own ultimate marker of the peak of the year comes from the natural world. There are in fact fewer striking signs of summer, in nature, than there are of the springtime, when everything is arriving or emerging or mating or breeding or desperately seeking food for young ones; by July, much of the race to reproduce has run its course. But there are some.

A splendid one is the formation by swifts of "screaming parties" in the evening, when the birds come together to perform a sort of ritual, ecstatic chase low down in the sky, screaming for all they are worth, screaming as loud as cats can yell, as they hurtle around roofs and the corners of buildings in a frenzy of display. My colleague Jeremy Laurance, The Independent's health editor, lives in swift territory in north London and in the evenings he has the screaming parties dashing through his garden; he is coming in to the office each morning now with stronger and stronger expressions of admiration and delight, pronouncing that "the swifts were sensational last night".

Another prominent marker of the hot days is, by contrast, silent and effectively stationary, and that is the arrival overhead, as night falls, of the "summer triangle". It consists of three stars, of pretty similar brightness (at least to the dullard eye like mine), Vega, Altair and Deneb, which are all in different constellations – for the record, Lyra, Aquila and Cygnus – but which form a hypothetical but unmistakable triangle in the night sky. Even star-watching beginners can pick it out with ease, not least because cold, blue Vega, often the first star to appear, is right above your head in summertime, and Cygnus is one of the most visible of the constellations (it's a swan flying down the Milky Way, and Deneb's in its tail).

But to find what is my own supreme summer symbol, you have to go to the woodlands, and be in the right place at the right time, and have a fair bit of luck. It's a butterfly; in fact it's one of a trio of high summer butterflies which for me go together like the three stars just mentioned. They're all magnificent, they're all inhabitants of old oak woods, and they're all on the wing between the end of June and the middle of July.

This year I went looking for them at Bookham Common in Surrey, a jewel of ancient woodland maintained with distinction by the National Trust, on the very edge of the commuter belt. I walked round with the warden, Ian Swinney, who knows every corner of the common and so might, I hoped, provide me with the bit of the right-place right-time luck I needed.

The first of the trio was immediately obvious: the silver-washed fritillary. Big as a child's hand, the males radiant orange, the females a little darker, they were nectaring on the brambles, the thistles and the burdock flowers along the woodland rides, so intent on their dose of sugar that you could put your nose right next to them. The second soon flitted into view: the white admiral. A long-winged insect like some of the tropical heliconid butterflies, its progress along the rides and round the brambles is distinctive: flap flap glide, flap flap glide. In a colour scheme limited to black and white, it is admirably well turned out; there were dozens of them, to my delight.

But of the third, the greatest prize, there was no sign. This is a creature which spends most of its time in the treetops and only rarely descends to the ground, and though Ian and I patrolled the woodland for the best part of three hours, there was no sign of it.

So rather than give you a personal account, the best I can do is show you a photo of one which, a couple of weeks ago, not only descended from the Bookham treetops, but descended on to Ian, and took up temporary residence on his boot, where he snapped it. And there you can see it, on the end of his leg – something which for me beats the beach and the barbecue as perhaps the most glorious of all the signs of high summer: the purple emperor.

How you can help these species survive

If you're fond of butterflies and you want to contribute to their conservation – 70 per cent of British species are declining – you can do so from this weekend by joining in the biggest-ever butterfly survey carried out by the public.

To take part in the Big Butterfly Count, run by the charity Butterfly Conservation, you only need to spend a quarter of an hour in a garden, park or field (or any location where butterflies might be seen) at any time between 24 July and 1 August, and make a note of what you see.

Learn more about it, and enter your records, on the website

The Natural Eye

Writing about wildlife art last week, I mentioned that Harriet Mead, the new president of the Society of Wildlife Artists, had renamed the society's annual exhibition. Stupidly, I gave the wrong name. The exhibition at London's Mall Galleries in September will be called The Natural Eye. My apologies to Harriet and to the Society.

For further reading

'Swifts', by Ted Hughes (in "Season Songs", Faber); 'Discover Butterflies in Britain', by David E Newland, (WildGuides, 2006)