In Wales, May 1 is a holiday known as Calan Mai or Calan Haf, which means the first day of summer. Celebrations start on the evening before, known as May Eve, with bonfires; as with Calan Gaeaf, the night before (Nos Galan Mai) is an Ysbrydnos, or "spirit night," when spirits are out and about and divination is possible. The tradition of lighting bonfires celebrating this occasion happened annually in south Wales until the middle of the 19th century. It is the Welsh equivalent of the Goidelic Beltane and one of a number of similar May Day traditions in Europe.
Read more about Calan Mai: Customs