Mating occurs mostly from mid-summer to early fall, mainly in late summer in central U.S. (Aldridge, 1993, J. Herpetol. 27:481-484), occasionally in spring. Young are born usually in August-October. Litter size increases with female size (average 5 where body size is small, maximum about 25 in the largest females where body size is large. Individual adult females may not give birth in some years, probably depending on nutritional status; interval between litters was 2 or more years in Wyoming (Graves and Duvall 1992). Requires several years to reach sexual maturity in areas with short growing season. Pregnant females may congregate in small area.