A collection of Red-eared Sliders observed at our neighborhood Beaver pond.
Wikipedia has this to say about Red-eared Sliders:
Some dimorphism exists between males and females.
Red-eared slider young look practically identical regardless of their sex, making it difficult to determine their sex. It is much easier to distinguish the sex of adults, as the shells of mature males are smaller than those of females when they reach maturity. Male red-eared sliders reach sexual maturity when their carapaces measure 10 cm and females reach maturity when their carapaces measure 15 cm. The male is normally smaller than the female, although this parameter is sometimes difficult to apply as individuals being compared could be of different ages. Males have longer claws on their front feet than the females; this helps them to hold on to a female during mating and is used during courtship displays. The male’s tail is thicker and longer. Typically, the cloacal opening of the female is at or under the rear edge of the carapace, while the male’s opening occurs beyond the edge of the carapace. The male’s plastron is slightly concave, while that of the female is totally flat. The male’s concave plastron also helps to stabilize the male on the female’s carapace during mating. The red marking on the males is also thought to be larger and brighter. Older males can sometimes have a dark greyish-olive green melanistic coloration, with very subdued markings. The red stripe on the sides of the head may be difficult to see or be absent. The female’s appearance is practically the same during all its life.
Both the male and female reach maturity at five to six years of age, but when kept in captivity, they do not hibernate and they feed more so they grow more rapidly and reach maturity slightly sooner than in nature.