The supercooling capacity and cold tolerance ofMusca domesticaL. embryos, larvae, prepupae, pupae, and adults were examined. Two-h-old embryos had the greatest supercooling capacity (−34°C) followed by 2-d-old pupae (−24°C), adults (−16°C), 1-d-old larvae (−15°C), and prepupae (−14°C). Significant differences (P≥ 0.001) between temperatures of crystallization means were observed among and within several stages. Age within a developmental stage was critical to survival at the treatment temperatures tested. The 50% mortality levels of the five developmental stages exposed to 10, 5, 0, and −5°C were determined and compared with the supercooling capacity. At temperatures above O°C, pupae were the most cold tolerant, followed by adults, larvae and prepupae, and embryos. However, at −5°C, 10- and 12-h-old embryos were able to tolerate the longest exposure, followed by pupae, larvae, prepupae, and adults. With this insect, the temperature of crystallization is not a reliable indicator of the lowest lethal temperature.