The red-eared slider or red-eared terrapin (Trachemys scripta elegans) is a subspecies of the pond slider (Trachemys scripta), a terrapin belonging to the family Emydidae. Native to the southern United States and extreme northern Mexico, it is popular as a pet across the world, and is the most invasive chelonian. It is the most commonly traded chelonian in the world. The red-eared slider is native to the central and southern United States and northern Mexico, but has become established in other places because of pet releases, and has become invasive in many areas where it outcompetes native species. The red-eared slider is included in the list of the world's 100 most invasive species.
Etymology
The red-eared slider gets its name from the small, red stripe around its ears, or where its ears would be, and from its ability to slide quickly off rocks and logs into the water. This species was previously known as Troost's turtle in honor of an American herpetologist Gerard Troost. Trachemys scripta troostii is now the scientific name for another subspecies, the Cumberland slider.
Taxonomy The red-eared slider belongs to the order Testudines, which contains about 250 chelonian species. It is a subspecies of Trachemys scripta. It was previously classified under the name Chrysemys scripta elegans. Trachemys scripta contains three subspecies: T. s. elegans (red-eared slider), T. s. scripta (yellow-bellied slider), and T. s. troostii (Cumberland slider).
Description
The carapace of this species can reach more than 40 cm (16 in) in length, but the typical length ranges from 15 to 20 cm (6 to 8 in). The females of the species are usually larger than the males. They typically live between 20–30 years, although some individuals can live for more than 40 years. Their life expectancy is longer when they are kept in captivity. The quality of their living environment has a strong influence on their lifespans and well being. The shell is divided into the upper or dorsal carapace, and the lower, ventral carapace or plastron. The upper carapace consists of the vertebral scutes, which form the central, elevated portion; pleural scutes that are located around the vertebral scutes; and then the marginal scutes around the edge of the carapace. The rear marginal scutes are notched. The scutes are bony keratinous elements. The carapace is oval and flattened (especially in the male) and has a weak keel that is more pronounced in the young. The color of the carapace changes depending on the age of the terrapin. It usually has a dark green background with light and dark, highly variable markings. In young or recently hatched terrapins, it is leaf green and gets slightly darker as a terrapin gets older, until it is a very dark green, and then turns a shade between brown and olive green. The plastron is always a light yellow with dark, paired, irregular markings in the centre of most scutes. The plastron is highly variable in pattern. The head, legs, and tail are green with fine, irregular, yellow lines. The whole shell is covered in these stripes and markings that aid in camouflaging an individual.
These terrapins also have a complete skeletal system, with partially webbed feet that help them to swim and that can be withdrawn inside the carapace along with the head and tail. The red stripe on each side of the head distinguishes the red-eared slider from all other North American species and gives this species its name, as the stripe is located behind the eyes, where their (external) ears would be. These stripes may lose their color over time. Color and vibrance of ear stripe can indicate immune health, with bright red having higher immune response than yellow stripes. Some individuals can also have a small mark of the same color on the top of their heads. The red-eared slider does not have a visible outer ear or an external auditory canal; instead, it relies on a middle ear entirely covered by a cartilaginous tympanic disc. Like other chelonians, the species is poikilothermic and thus dependent on the temperature of its environment. For this reason, it needs to sunbathe frequently to warm up and maintain body temperature.
Sexual dimorphism
Some dimorphism exists between males and females. Red-eared slider young look practically identical regardless of their sex, making distinguishing them difficult. One useful method, however, is to inspect the markings under their carapace, which fade as the terrapins age. Distinguishing the sex of adults is much easier, as the shells of mature males are smaller than those of females. 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 about 15 cm (5.9 in). Both males and females reach sexual maturity at 5–6 years old. Males are normally smaller than females, 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 onto a female during mating, and is used during courtship displays. The males' tails are thicker and longer. Typically, the cloacal opening of a 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. 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.
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