Ice Saints
Updated: Wikipedia source
The Ice Saints are Mamertus, Pancras of Rome, Servatius of Tongeren and Boniface of Tarsus. They are so named because their feast days fall on the days of May 11, May 12, May 13 and May 14 respectively, which often saw the last cold snap of the season. In some countries, only three are included in the Ice Saints, and Sophia of Rome (May 15) can be added in some areas. In the United Kingdom, the term 'blackthorn winter' is an old phrase originating in rural England to describe a cold period in early spring when blackthorn is in flower.