Determining the sex of reptiles can be much trickier than sexing mammals. These animals carry most of their sexual characteristics inside their bodies. However, make and female red-ear sliders do have some visible differences between them. Once a young turtle reaches the correct size, it's possible to determine its sex with some accuracy.
Very young turtles usually cannot be sexed accurately, as they don't yet show major differences between male and female. A young turtle must be at least 3 to 4 inches long before accurate sexing is possible. Female red-ear sliders are usually larger than males, but have a smaller, thinner tail and shorter front claws. Overfed turtles may grow more quickly and reach sexual maturity faster than animals that receive normal diets.
There is no set age for young red-ear sliders to reach sexual maturity. Captive turtles often grow more quickly than wild ones and reach maturity faster. According to the Red-Ear Slider website, males are likely to reach 4 inches between the ages of 2 and 4, while females of that age are often an inch longer. Trying to sex these animals earlier rarely yields reliable results.
Turtles all have a single opening, called the cloaca or vent, which serves both for excretion and reproduction. Male red-ear sliders have a much longer tail than females, and the cloaca is positioned lower on the tail. In females, the cloaca is close to the body, while males have a cloaca located almost at the tip of the tail.
Sexing red-ear sliders becomes easier as the turtles age. In older males, the nose and snout are longer, and the end of the plastron, the ventral part of the shell, is partially concave to provide stability during mating. These features are present in young turtles, but are generally too subtle to notice. Owners who have trouble determining whether their turtles are male or female may have better results if they wait a few months, then try again.
After sexual maturity, female red-ear sliders may lay eggs or present laying behavior, even if males are not present. Turtles that are laying eat less and may be more active. Digging is especially common, especially in cages with appropriate nesting materials such as peat moss or potting soil. Males do not display this behavior.