Funeral service for Mrs. Mary Ahrens, 80, 1035 Culebra St., who died Thursday, will be held at 2 p.m. Saturday at Riebe Funeral Home, with the Rev. Vernon Mohn officiating.  Interment will be in the Helotes Cemetery.  Survivors are: husband, Edward Ahrens; daughters, Miss Elizabeth Ahrens, Mrs. Sam Benke, and Mrs. Ralph Bottriell, all of San Antonio; Mrs. George Spoo, Iowa; Mrs. Clarence Coss, San Angelo; sons, Willie, Harry, Alfred and Adolph Ahrens, all of San Antonio; brother, Joe Rittiman, Boerne.