It’s the Early May Bank Holiday in Scotland today. Ian Wiki confirms that May Day is an ancient northern hemisphere spring festival.
The earliest May Day celebrations appeared in pre-Christian times, with the Floralia, festival of Flora.
In explaining the origins of May Day, Ian comes up with all sort of specifics, but kind of slides over the idea that – as Longsufferingreaderoftheblogpaul wrote in a comment to a particularly off-the-wall post – time is social. Harvests. Day and night. Diurnal clocks. Biorhythms and cycles. All that mushy wetware bio stuff I never learned but is real.
Cornwall in England definitely gets into that side of things:
[On May Day,] Padstow holds its annual Hobby Horse day of festivities, believed to be one of the oldest fertility rites in the UK.