The red-eared slider originated from the area around the Mississippi River and the Gulf of Mexico, in warm climates in the southeastern corner of the United States. Their native areas include the southeast of Colorado, Virginia, and Florida. In nature, they inhabit areas with source of still, warm water, such as ponds, lakes, swamps, creeks, streams, or slow-flowing rivers. They live in areas of calm water where they are able to leave the water easily by climbing onto rocks or tree trunks so they can warm up in the sun. Many individuals are often found sunbathing together in a group or even on top of each other. They also require abundant aquatic plants, as this is the adults' main food, although they are omnivores. Turtles in the wild always remain close to water unless they are searching for a new habitat or when females leave the water to lay their eggs.
Owing to their popularity as pets, red-eared sliders have been released or escaped into the wild in many parts of the world. Feral populations of red-eared sliders are now found in Australia, Europe, South Africa, the Caribbean, Israel, Bahrain, Mariana Islands, Guam, and southeast and far east Asia. In Australia, it is illegal for members of the public to import, keep, trade, or release red-eared sliders, as they are regarded as an invasive species. Their import has been banned by the European Union and specific member countries. Invasive red-eared sliders cause negative impacts in the ecosystems they occupy because they have certain advantages over the native populations, such as a lower age at maturity, higher fecundity rates, and larger body size, which gives them a competitive advantage at basking and nesting sites, as well as when exploiting food resources. They also transmit diseases and displace the other turtle species with which they compete for food and breeding space.
For many years, Aussies have been valued by stockmen for their versatility and trainability. They have a similar look to the popular English Shepherd and Border Collie breeds. While they continue to work as stock dogs and compete in herding trials, the breed has earned recognition in other roles due to their trainability and eagerness to please and are highly regarded for their skills in obedience. Like all working breeds, the Aussie has considerable energy and drive and usually needs a job to do. It often excels at dog sports such as dog agility, flyball, and frisbee. They are also highly successful search and rescue dogs, disaster dogs, detection dogs, guide dogs, service dogs, and therapy dogs.
Red-eared sliders are almost entirely aquatic, but, as they are cold-blooded, they leave the water to sunbathe to regulate their temperature.
They are excellent swimmers. When they are out of the water, they remain alert and flee from any predators or from humans. On sensing a threat, they rapidly launch themselves back into the water. During the day, they usually alternate between warming themselves in the sun and spending time in the water.
They can become aggressive if they become overcrowded or if the ratio of the sexes is not balanced. In captivity, a ratio of two or three females per male is usually recommended.
Reptiles do not hibernate, but actually brumate, as they become less active, but occasionally rise to the surface for food or air. Brumation can occur to varying degrees. Red-eared sliders brumate over the winter at the bottom of ponds or shallow lakes; they become inactive, generally, in October, when temperatures fall below 10 °C (50 °F). During this time, the turtles enter a state of sopor, during which they do not eat or defecate, they practically do not move, and the frequency of their breathing falls. Individuals usually brumate under water, but they have also been found under banks and hollow stumps and rocks. In warmer winter climates, they can become active and come to the surface for basking. When the temperature begins to drop again, however, they will quickly return to a brumation state. Sliders will 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. The lactic acid produced is buffered by minerals in the shell, preventing acidosis. Red-eared sliders kept captive indoors should not brumate.
The red-eared slider is the most common type of water turtle kept as pets. As with other turtles, tortoises, and box turtles, individuals that survive their first year or two can be expected to live generally around 30 years. Red-eared sliders can be quite aggressive—especially when food is involved. Behavior is usually noted to become this way when fed live food. If being kept as a pet, care must be taken to prevent injury or even death of smaller tank mates. Additional care is needed if shrimp are used as food. Smaller red-eared sliders less than a year old have been known to choke on the shells of the shrimp and suffer from lung puncture.