Mayday corresponds with the Irish festival of La Bealtaine, which officially heralded the beginning of the summer. It was surrounded by a large number of folk
A good link with some info on may day Piseogs.
In mythology the Tuatha de Danann come ashore at Bealtaine and heros like Cu Chulainn are born. Lots of good and bad things happen at this time of year in folk stories too. The fairies move from their winter house to their summer house and anything can happen.
You can fall asleep by a tree or ringfort and learn a song. You can come across fairies playing a game at night and get the gift of bone setting by helping out anyone that gets injured. You can also be harmed by them and theyll test you to see if your greedy, selfish or lazy and punish you accordingly. Maybe even kill you.
The fairies moving about at this time of year is mimicking the transhumance called Booleying that used to be traditional in Ireland. There are indigenous nomadic ethnicities in ireland today but we were all a lot more like the travellers once.