While the name Walpurgis is taken from the eighth-century English missionary Saint Walburga, "Valborg", as it is called in Swedish, has very little to do with religion and everything to do with the arrival of spring. The forms of celebration vary in different parts of the country and between different cities. Walpurgis celebrations are not a family occasion but rather a public event, and local groups often take responsibility for organizing them to encourage community spirit in the village or neighborhood.

Walpurgis bonfires are part of a Swedish tradition dating back to the early 18th century. At Walpurgis (Valborg), farm animals were let out to graze and bonfires (majbrasor, kasar) lit to scare away predators. In southern Sweden, an older tradition, no longer practiced, was for the younger people to collect greenery and branches from the woods at twilight. These were used to adorn the houses of the village. The expected reward for this task was to be paid in eggs.

(from Wikipedia)