Red-eared slider

Male red-eared slider: Note the large claws on the front foot

Some dimorphism exists between males and females.[11]

Red-eared slider young look practically identical regardless of their sex, making it difficult to distinguish them. One useful method, however, is to inspect the markings under their carapace, which fade as the turtles age. It is much easier to distinguish the sex of adults, as the shells of mature males are smaller than those of females.[12] Male red-eared sliders reach sexual maturity when their carapaces' diameters measure 10 cm (3.9 in) and females reach maturity when their carapaces measure 15 cm. Both male and females reach sexual maturity at five to six years. 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.[13] 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 completely flat. The male's concave plastron also helps to stabilize the male on the female's carapace during mating.[14] 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 substantially the same throughout her life.

Red-eared sliders do not hibernate, but actually brumate; while they become less active, they do occasionally rise to the surface for food or air. Brumation can occur to varying degrees. In the wild, red-eared sliders brumate over the winter at the bottoms of ponds or shallow lakes. They generally become inactive in October, when temperatures fall below 10 °C (50 °F).[9] During this time, the turtles enter a state of sopor, during which they do not eat or defecate, they remain nearly motionless, and the frequency of their breathing falls. Individuals usually brumate underwater, but they have also been found under banks and rocks, and in hollow stumps. In warmer winter climates, they can become active and come to the surface for basking. When the temperature begins to drop again, however, they quickly return to a brumation state. Sliders generally come up for food in early March to as late as the end of April.

During brumation, T. s. elegans can survive anaerobically for weeks, producing ATP from glycolysis. The turtle's metabolic rate drops dramatically, with heart rate and cardiac output dropping by 80% to minimise energy requirements.[26][27] The lactic acid produced is buffered by minerals in the shell, preventing acidosis.[28] Red-eared sliders kept captive indoors should not brumate.

Red-eared slider sunbathing: Heat absorption is more effective when their limbs are stretched outwards.

Hatching turtle with its egg tooth

Female laying eggs in a nest she dug out with her hind legs

Courtship and mating activities for red-eared sliders usually occur between March and July, and take place under water. During courtship, the male swims around the female and flutters or vibrates the back side of his long claws on and around her face and head, possibly to direct pheromones towards her.[29] The female swims toward the male and, if she is receptive, sinks to the bottom for mating. If the female is not receptive, she may become aggressive towards the male. Courtship can last 45 minutes, but mating takes only 10 minutes.[25]

A pair of red-eared sliders.

On occasion, a male may appear to be courting another male, and when kept in captivity may also show this behaviour towards other household pets. Between male turtles, it could be a sign of dominance and may preclude a fight. Young turtles may carry out the courtship dance before they reach sexual maturity at five years of age, but they are unable to mate.[30]

After mating, the female spends extra time basking to keep her eggs warm.[30] She may also have a change of diet, eating only certain foods, or not eating as much as she normally would. A female can lay between two and 30 eggs depending on body size and other factors.[18] One female can lay up to five clutches in the same year, and clutches are usually spaced 12 to 36 days apart.[31] The time between mating and egg-laying can be days or weeks. The actual egg fertilization takes place during the egg-laying. This process also permits the laying of fertile eggs the following season, as the sperm can remain viable and available in the female's body in the absence of mating. During the last weeks of gestation, the female spends less time in the water and smells and scratches at the ground, indicating she is searching for a suitable place to lay her eggs. The female excavates a hole, using her hind legs, and lays her eggs in it.[32]

Incubation takes 59 to 112 days.[18] Late-season hatchlings may spend the winter in the nest and emerge when the weather warms in the spring. Just prior to hatching, the egg contains 50% turtle and 50% egg sac. A new hatchling breaks open its egg with its egg tooth, which falls out about an hour after hatching. This egg tooth never grows back. Hatchlings may stay inside their eggshells after hatching for the first day or two. If they are forced to leave the eggshell before they are ready, they will return if possible. When a hatchling decides to leave the shell, it still has a small sac protruding from its plastron. The yolk sac is vital and provides nourishment while visible, and several days later it will have been absorbed into the turtle's belly. The sac must be absorbed, and does not fall off. The split must heal on its own before the turtle is able to swim. The time between the egg hatching and water entry is 21 days.

Damage to or inordinate motion of the protruding egg yolk, enough to allow air into the turtle's body, results in death. This is the main reason for marking the top of turtle eggs if their relocation is required for any reason. An egg turned upside down will eventually terminate the embryo's growth by the sac smothering the embryo. If it manages to reach term, the turtle will try to flip over with the yolk sac, which would allow air into the body cavity and cause death. The other fatal danger is water getting into the body cavity before the sac is absorbed completely and while the opening has not completely healed yet.

The sex of red-eared sliders is determined by the incubation temperature during critical phases of the embryos' development. Only males are produced when eggs are incubated at temperatures of 22–27 °C (72–81 °F), whereas females develop at warmer temperatures.[33] Colder temperatures result in the death of the embryos.

A line of basking red-eared sliders faces an inquisitive mallard.

Reptiles are asymptomatic (meaning they suffer no adverse side effects) carriers of bacteria of the genus Salmonella.[37] This has given rise to justifiable concerns given the many instances of infection of humans caused by the handling of turtles,[38] which has led to restrictions in the sale of red-eared sliders in the USA. A 1975 U.S. Food and Drug Administration (FDA) regulation bans the sale (for general commercial and public use) of both turtle eggs and turtles with a carapace length of less than 4 in (10 cm). This regulation comes under the Public Health Service Act, and is enforced by the FDA in cooperation with state and local health jurisdictions. The ban was enacted because of the public health impact of turtle-associated salmonellosis. Turtles and turtle eggs found to be offered for sale in violation of this provision are subject to destruction in accordance with FDA procedures. A fine of up to $1,001 and/or imprisonment for up to one year is the penalty for those who refuse to comply with a valid final demand for destruction of such turtles or their eggs.[39] Many stores and flea markets still sell small turtles due to an exception in the FDA regulation which allows turtles under 4 in (10 cm) to be sold "for bona fide scientific, educational, or exhibition purposes, other than use as pets."[40] As with many other animals and inanimate objects, the risk of Salmonella exposure can be reduced by following basic rules of cleanliness. Small children must be taught to wash their hands immediately after they finish playing with the turtle, feeding it, or changing its water.

Some states have other laws and regulations regarding possession of red-eared sliders because they can be an invasive species where they are not native and have been introduced through the pet trade. Now, it is illegal in Florida to sell any wild-type red-eared slider, as they interbreed with the local yellow-bellied slider population — Trachemys scripta scripta is another subspecies of pond sliders, and hybrids typically combine the markings of the two subspecies. However, unusual color varieties such as albino and pastel red-eared sliders, which are derived from captive breeding, are still allowed for sale.[41]

In Australia, breeding populations have been found in New South Wales and Queensland, and individual turtles have been found in the wild in Victoria, the Australian Capital Territory and Western Australia.[42]

Red-eared slider turtles are considered a significant threat to native turtle species – they mature more quickly, grow larger, produce more offspring and are more aggressive.[42] Numerous studies provide evidence that red-eared slider turtles can out-compete native turtles for food and nesting and basking sites.[43] Because red-eared slider turtles eat plants as well as animals, they could also have a negative impact on a range of native aquatic species, including rare frogs.[44] There is also a significant risk that red-eared slider turtles will transfer diseases and parasites to native reptile species. There is evidence that a malaria-like parasite was spread to two wild turtle populations in Lane Cove River, Sydney.[45]

Social and economic costs are also likely to be substantial. The Queensland government has invested close to $1 million AUD in eradication programs to date.[42] As outlined in the foregoing section, the turtle may also have significant public health costs due to the impacts of turtle-associated salmonella on human health. Outbreaks in multiple states and fatalities in children, associated with handling salmonella-infected turtles, have been recorded in the USA.[46] Salmonella can also spread to humans when turtles contaminate drinking water.[47]

There have been varying degrees of action by state governments to date, ranging from ongoing eradication efforts by the Queensland government to very little action by the government of New South Wales.[48] Experts have ranked the species as high priority for management in Australia and are calling for a national prevention and eradication strategy, including a concerted education and compliance program to stop the illegal trade, possession and release of slider turtles.[49]