On the sunlit chalk downlands of southern England, a flitting bright-blue butterfly poses an identification puzzle. Could it be an adonis blue? A chalkhill blue? A common blue? I am not on the sunlit chalk downlands of southern England. I am among brambles, in a sloping reach of untended land that separates the train station from the waters of Bradford Beck, at one time the most polluted river in England. This butterfly – jinking low across the tops of the brambles and brackens – can only be a common blue. There’s something to be said for narrow horizons, a trammelled perspective. It’s the only blue I’ve seen around here this summer. These days we all like to talk up the edgelands, the wilderness of the unnoticed, so vibrant, so enigmatic – which is great, but at the same time it’s worth recognising that in these dank lands of buddleia and balsam, elder and hawthorn, graffiti tags and dog-poo bags, we’re pretty unlikely to meet anything really out of the ordinary, anyone other than the same old lags. Ringlet butterflies, whites, tortoiseshells, orange-tips, the odd red admiral, bringing the drama. The most exotic bird here is the chiffchaff, shortly Africa-bound but still two-stepping relentlessly in the buckled ash trees. The trick, of course, is to take your small joys where you can. The blue lands lightly on a bramble leaf and shivers as it stretches out its wings. Against the downbeat matt tones of the September foliage, it’s a startling, double-take blue, the blue of a bright late-afternoon sky, a Paul Newman’s-eyes blue. To someone who’s not very good with butterflies, but even worse with wildflowers, it’s fascinating to look up a butterfly’s food plants in the field guide and feel a previously undisclosed ankle‑height ecosystem opening up to you. The common blue favours bird’s-foot trefoil, the orange-tip cuckooflower or garlic mustard – who knew we had such things, out here? Well, the butterflies did, of course. Though it’s worth pointing out that in this case, too, our wrong-side-of-the-tracks wildlife embraces a sort of reversion to the mean: most of the butterflies here are perfectly happy with stinging nettles, of which we have a rich profusion. Country diary is on Twitter/X at @gdncountrydiary Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024 (Guardian Faber) is published on 26 September; pre-order now at the guardianbookshop.com and get a 20% discount