For several years, I’ve made a pilgrimage to a single, indeed the only, buddleia bush I know in this part of the Manifold Valley, and each visit has produced encounters with silver-washed fritillaries. Not only is this butterfly one of the grandest of Europe’s 50 fritillary species, it is also immensely beautiful. The wings’ upper surfaces are flame-orange incised with black lines and ringed at the rear margin by solid black spots. Imagine a cheetah’s flanks and you would have only a muted version of that colour pattern, because “flame” doesn’t quite do justice to the full temperature of the butterfly’s hue, which is more magma than fire. The upper wings are brilliant, but the undersides are perhaps the more compelling. A subtle marbling of those same base colours is arranged around a plane of lichen green that is traversed by wavering tide-lines of white – the so-called “silver” of its name. There is a final gloss to these butterfly outings because the first one I found was among the first regional records for decades. The fritillary was here until the 1940s, but underwent a severe range contraction southwards and vanished entirely from eastern England. Last century, it began a slow recolonisation, and filled in many old Midlands and East Anglian haunts, while sightings as far north as Newcastle suggest the advance is ongoing. Autumn records involve post-breeding individuals at the end of their flight period. With frayed wings and faded colours, the insects look worn, and even the buddleia is often wind-battered, the heavy-ended spears of lavender scatter their delicate lode of nectaring butterflies as they sway. Red admirals, peacocks and commas all circle the branches, and every now and then, in comes the fritillary, swooping down through the canted light, wings winking in and out as they cross the lines of afternoon shadow. While its proboscis jabs one well of buddleia nectar after another, I close slowly to touching distance. I can pick out even the tiny flecks of black on its green compound eyes and wonder what labyrinth of colour and sweetness shapes the inner world of this marvellous being. 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