This is the ancient feast of Ss. Philip and James the Less, apostles. They’re associated with red spring flowers: the tulip for St. Philip (so you know it’s not that old a tradition), and red bachelor’s buttons or campion for St. James the Less.
St. James the Less is the guy who was known for his camel knees (ie, he prayed so much that his knees got messed up), and who was murdered at the Temple in AD 62. Even a lot of Jewish people who didn’t like Christians were sure that James was a holy man, so this was a controversial move.
St. Philip was martyred in Phrygia.
This was the day when the English “fetched home the May” from the woods. Literally, a may tree is a kind of hawthorn that blossoms white in the spring. May was also a guy, and his bride was Flora (hence “the Floral Dance”). May was also sometimes the Maypole itself, although other towns kept a good Maypole all year round. (Obviously the right kind of tree might not be easy to find.) Dancing around the Maypole followed the fun of bringing back the May. The whole day was a holiday, so a lot of young couples spent the day together. You also brought home flowers from the woods, so leaving flowers or May Day baskets at the houses of older people was a thing.
May Day was also associated with “May games,” which were generally elaborate pageants s that might include skits, dances, sports, athletic contests, and games. They were often associated with Morris dancing, hobby horse dancing, and retelling of legends of Robin Hood and Maid Marian (who often presided over the whole thing). In other places, maskers in May outfits go to people’s houses to dance and sing.
Many Maypoles were destroyed or burned as “idols” by anti-Catholic or anti-dancing Protestants or Puritans, although some survived in rural places. In 1644, all maypoles were outlawed in the British Isles. But when King Charles II came in, maypoles returned, and they put up one 134 feet high in the Strand in London.
In a lot of places after Charles II, May celebrations were overseen by the Anglican clergy, to prevent Mayers being messed with. There were also versions of May songs which deflected criticism by adding LOTS AND LOTS of Christian content. (But not Catholic content! No!)
For example, here’s “The Mayer’s Song” from Hitchin, Hertfordshire, from Hone’s Every-Day Book.
Remember us poor Mayers all, and thus we do begin
To live our lives in righteousness, or else we die in sin.
We have been rambling all this night, and almost all this day,
And now return-ed back again, we bring you a branch of may.
A branch of may we have brought you, and at your door it stands,
It is but a sprout, but it’s well-budded out by the work of Our Lord’s hands.
The hedges and trees, they are so green, as green as any leek,
Our Heavenly Father, He watered them with His heavenly dew so sweet.
The heavenly gates are open wide, our paths are beaten plain,
And if a man be not too far gone, he may return again.
The life of man is but a span, it flourishes like a flower,
We are here today and gone tomorrow, and we are dead in an hour.
The Moon shines bright, and the stars give a light, a little before it is day,
So God bless you all, both great and small, and send you a joyful May!
There are a lot of May carol variants on this, and here’s one on Youtube.
In more recent times, May Day was taken over by the Communists in some countries, which led to Pope Pius XII making a feast of St. Joseph the Worker and moving it onto May 1, with Philip and James getting moved to May 3.
Of course May is also one of Mary’s big months, so you find people doing May Crowning of statues of Mary during this month. This year, Pope Francis has called for even more May rosary devotions than normal, so I’m sure that will be a thing. (Probably because we’re all worried about schism in Germany.)