Based on overwintered pupal survival to heat stress, unusually hot periods have been suggested as a primary factor for the southern range limit of Papilio canadensis. However, while summer and fall temperatures may be high enough to induce pupal stress, springtime temperatures at the P. canadensis southern range limit are lower than the temperatures necessary to induce significant stress. In this study we tested whether pupal stress due to high temperatures is a likely determinant of the southern limit of P. canadensis. We exposed pupae of P. canadensis (N=270 pupae) and it’s sibling species P. glaucus (N=270 pupae) to high temperatures during the fall (zero, one, or two weeks with 37 °C days and 22 °C nights 12:12 D:N) and warm (24 °C days, 18 °C nights 18:6 D:N) or cool (16 °C days, 10 °C nights 18:6 D:N) spring emergence conditions. In addition, the effect of prolonged warm temperatures (14 °C, 18 °C, 22 °C, and 26 °C) prior to the onset of winter on P. canadensis pupae was recorded (N=383). Pupal condition based on weight and size was recorded prior to temperature treatments and after overwintering. The condition of emerging butterflies was determined based on weight, body size, and wing length of each emerging butterfly. Results indicate that temperature does induce a significant cost on P. canadensis, however not enough to limit the range of P. canadensis. We speculate that a higher fitness of P. glaucus relative to P. canadensis in southern latitudes is the cause of the southern range limit of P. canadensis.