Valborg (May day)

The festival is named after Saint Walburga (known in Scandinavia as "Valborg"; alternative forms are "Walpurgis", "Wealdburg", or "Valderburger"), born in Wessex in 710. She was a niece of Saint Boniface and, according to legend, a daughter to the Saxon prince St. Richard. Together with her brothers she travelled to Frankonia, Germany, where she became a nun and lived in the convent of Heidenheim, which was founded by her brother Wunibald. Walburga died on 25 February 779 and that day still carries her name in the Catholic calendar. However she was not made a saint until 1 May in the same year, and that day carries her name in the Swedish calendar.
Historically the Walpurgisnacht is derived from Pagan spring customs, where the arrival of spring was celebrated with bonfires at night. Viking fertility celebrations took place around April 30 and due to Walburga being declared a saint at that time of year, her name became associated with the celebrations. Walburga was honored in the same way that Vikings had celebrated spring and as they spread throughout Europe, the two dates became mixed together and created the Walpurgis Night celebration.

Walpurgis is one of the main holidays during the year in both Sweden and Finland, alongside of Christmas and Midsummer. The forms of celebration in Sweden vary in different parts of the country and between different cities. One of the main traditions in Sweden is to light large bonfires, a custom which is most firmly established in Svealand, and which began in Uppland during the 18th century. An older tradition from Southern Sweden was for the younger people to collect greens and branches from the woods at twilight, which were used to adorn the houses of the village. The expected reward for this task to be paid in eggs.
The tradition which is most spread throughout the country is probably singing songs of spring. Most of the songs are from the 19th century and were spread by the students' spring festivities. The strongest and most traditional spring festivities are also found in the old university cities, like Uppsala and Lund where both current and graduated students gather at events that take up most of the day from early morning to late night on April 30, or "sista april" ("The last day of April") as many people call it. There are also newer student traditions like the carnival parade, The Cortège, which has been held since 1909 by the students at Chalmers in Gothenburg. In Sweden, Valborg is especially notorious because of the excessive amounts of alcohol people consume on that very day.
http://en.wikipedia.org/wiki/Walpurgis_Night