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.
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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.