ðeɪ ɑːɹ sˌoʊ nˈeɪmd bɪkˈʌz ðɛɹ fˈiːst dˈeɪz fˈɔːl ɔnðə dˈeɪz ʌv mˈeɪ ɪlˈɛvən, mˈeɪ twˈɛlv, ænd mˈeɪ θˈɜːtiːn ɹᵻspˈɛktɪvli, nˈoʊn æz ðə blˈækθɔːɹn wˈɪntɚɹ ɪn ˈɔːstɹiən, bˈɛldʒən, kɹoʊˈeɪʃən, tʃˈɛk, dˈʌtʃ, fɹˈɛntʃ, dʒˈɜːmən, hʌŋɡˈɛɹiən, nˈɔːɹθɪtˈæliən, pˈoʊlɪʃ, slˈoʊvæk, slˈoʊviːn ænd swˈɪs fˈoʊkloːɹ.
They are so named because their feast days fall on the days of May 11, May 12, and May 13 respectively, known as the blackthorn winter in Austrian, Belgian, Croatian, Czech, Dutch, French, German, Hungarian, North-Italian, Polish, Slovak, Slovene and Swiss folklore.