or Frost Saints. Those saints whose days fall in what is called “the blackthorn winter” —that is, the second week in May (between li and 14). Some give only three days, but whether 11, 12, 13 or 12, 13, 14 is not agreed. May 11th is the day of St. Mamertus, May 12th of St. Pancratius, May 13th of St. Servatius, and May 14th of St. Boniface.
“Ces saincts passent pour saincts gresleurs, geleurs, et gateurs du bourgeon.” —Rabelais.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894