Ice Saints – The Ice Saints are St. Mamertus (or, in some countries, St. Boniface of Tarsus), St. Pancras, and St. Servatius. They are so named because their feast days fall on the days of May 11, May 12, and May 13 respectively, known as “the black-thorn winter” in Austrian, Belgian, Croatian, Czech, Dutch, French, German, Hungarian, North-Italian, Polish, Slovakian, Slovene and Swiss folklore.