The 'butter-coloured fly' is the theory, first put forward as early as the 18th century when butterflies were still known, as they had been in classical times, as 'flies' and their caterpillars as 'worms'. I should add that the butterfly was also more respectfully described by the ancient Greeks as psyche, the same word as 'spirit', because of the marvel of the adult insect emerging from the chrysalis just as the soul may do from the grave.
To me, the Brimstone is more of a lemony or even limey fly. Perhaps we should campaign for an etymological (and entomological) change to Lemonfly, though I fear that it would be as unsuccessful as Sir Isaac Pitman's use of his shorthand royalties to promote phonetic spelling. Kingston Buildings' old street sign in Bath, reading something like Kingstn Bildingz, was the solitary memorial to this project in my days as a young journalist on the then Evening Chronicle. The Chron is a weekly now and I'm not sure if the sign is still there.
In the same colourway as the Brimstone, behold those mighty ragwort-munchers, Cinnabar Moth caterpillars whose vivid colour combo warns predators that they are poisonous ann enables them to gorge themselves openly. I have defended ragwort before and do so again now. Any fair-minded person spending a bit of time on Google will come to the conclusion, I am sure, that calls for its elimination as a supposedly dangerous weed are ill-judged.
|The Hedge Brown - usually a bit shy of opening its wings to show the bright orange, but this one was helpful|
Apart from the Brimstone, I saw nine of the UK's 60-odd kinds of butterfly in the garden sunshine yesterday: there were Small, Large and Green-veined Whites in profusion, lots of Ringlets, Meadow Browns and Hedge Browns (also known as Gatekeepers, both names due to their fondness for the edges and hedges of fields), a lofty Peacock, a darting Comma, and a Red Admiral. This looks like being a very good summer after an extremely poor one last year and I don't think we need rocket science to see why. It's the sun what's done it.
|A Green-veined White. On close inspection, the 'green' is more of a dusting of little black and grey specks|