The Ice Saints is the name given to St. Mamertus, St. Pancras, and St. Servatius in Hungarian, German, Austrian, and Swiss folklore. They are so named because their feast days fall on the days of May 11, May 12, and May 13 respectively. The period from May 12 to May 15 was noted to bring a brief spell of colder weather in the Northern Hemisphere under the Julian Calendar. With the change to the Gregorian Calendar, however, the equivalent days would be May 19–May 22.
In Poland, the Ice Saints are St. Pancras, St. Servatus and St. Boniface; St. Boniface's feast day falling on May 14. The trio are known collectively as the 'cold gardeners', the three days culminating in 'Zimna Zośka' (Cold Sophia's), the feast day of St. Sophia which falls on May 15.
In Sweden, the German legend of the ice saints has resulted in the belief that there are special "iron nights", especially in the middle of June, which are susceptible to frost. The term "iron nights" (järnnätter) has probably arisen through a mistranslation of German sources, where the term "Eismänner" (ice men) was read as "Eisenmänner" (iron men) and their nights then termed "iron nights", which then became shifted from May to June.