Critter Corner No. 18
The Red-eared Slider
Sherman Minton’s authoritative Amphibians & Reptiles of Indiana (1) notes that this turtle emerges, in southern Indiana, from its period of winter inactivity in early April. But, this book was published in 2001. In our rapidly warming world, Mother Nature seems to be re-writing the rules. By mid-February 2017, large numbers of Pond Sliders were to be seen basking in the afternoon sun in nearly every pond, marsh, and stripper pit in the area. Of course Mother Nature can still throw a wicked curve ball and our recent reminder that it is still officially winter had the turtles heading for cover again.
Lying upon a favorite log or snag as pond sliders do is an example of what is known as thermoregulatory behavior. Since turtles, like other reptiles, are ectotherms they do not have the internal physiological mechanisms by which they might maintain a high, stable body temperature as we do. Since the rate at which metabolic activities (neuromuscular activity, digestion, assimilation, etc.) is related directly to temperature, it behooves the turtles to raise their body temperature above that of the surrounding air and water. The basking in which we see them engaged allows them to be much more efficient in searching for food, escaping predators, and performing other daily activities .Although ectothermic, reptiles can by means of a repertoire of behaviors (basking, shade-seeking, water immersion) maintain a relatively high, static body temperature in relationship to the highly variable ambient temperature around them. Consistent, extremely low temperatures are their main bugaboo. Thus, as we move from the equator to the poles, we see a graded decline in the number of species of reptiles endemic to a given latitude.
Red-eared Sliders bear the scientific moniker of Trachemys scripta elegans. Their genus name (Trachemys) comes from Greek words meaning “rough” and “freshwater tortoise”(2). Nowadays we reserve the term tortoise for a particular group of land turtles but you get the idea – a water, dwelling turtle with a rough carapace. The species name scripta (script) refers to the markings upon the carapace. By placing a third name after the scientific name taxonomists are noting that elegans (fine or elegant) is a subspecies. Biologists typically recognize three subspecies of Pond Slider, the red-eared found in our area as well as the Yellow-bellied (SE U.S.) and the Cumberland Slider (ENE TN & SW VA).
Incidentally, if one refers to Minton’s book, the scientific name will be followed by, in parentheses, the name Wied; in other references it may be Wied-Neuwied. This is an interesting example of history entwining itself with biology. The name refers to Prince Maximilian of Wied-Neuwied, a 19th Century German explorer, ethnologist, and naturalist (3). Wied-Neuwied was mentored by the renowned naturalist Alexander von Humboldt who, by the way, is the subject of the recent bestseller The Invention of Nature by Andrea Wulf. Wied-Neuwied led two expeditions to the New World, one to Brazil and the other to the United States (4). During the latter trip he was accompanied by the Swiss artist Karl Bodmer, now famous for his paintings of Native Americans done during this expedition. In October of 1832, en route to the west, the Prince arrived in New Harmony, Indiana. At that time, New Harmony was known as a center of education and scientific research. During his time there, he observed and named the Red-eared Slider as well as two frog species (5). This is why Wied’s name appears after the turtle’s scientific name in Minton.
At Goose Pond FWA, the Red-eared Slider is one of the more common species. They can often be seen basking on the muskrat lodges which are abundant in standing waters of the property. During the 2010 Biodiversity Survey of the GPFWA, numerous turtle nests were found on the so-called “double-ditches” peninsula. Most of these were thought to contain T. scripta clutches. A very high percentage of them had been found by predators, most likely raccoons, and destroyed. An average clutch size for this species is around 10 eggs (6 to 30 may be laid). The incubation period is two months or a little more and, like many other turtles, the sex of the offspring is determined by incubation temperature. Warmer temperatures (>80F or so) produce females (6). Mating occurs in late spring or early summer. Males and females may be distinguished from one another but the differences are subtle and include features such as claw length and overall size of the upper shell. The strong similarities of the two sexes may remind us of Ogden Nash’s poetic thoughts on turtle sexual dimorphism.
The turtle lives ‘twixt plated decks
Which practically conceal its sex.
I think it clever of the turtle
In such a fix to be so fertile.
Red-eared Sliders are omnivorous, that is both plant and animal material may be consumed by them. Plants such as duckweed and emergent pondweeds are eaten while animal prey includes snails, crayfish, aquatic insects, tadpoles, and fish.
You may recall times past when it was exceedingly common to see young Red-eared Sliders for sale in various pet stores or “five & dimes”. Their attractive appearance and abundance made this species a prime candidate for exploitation. They are far and away the most popular turtle pet. This has created significant problems in many areas of the world. Baby sliders, most farm-raised, have been shipped to states, and countries, outside their native range. As you might guess, turtles that end up released into the wild cause ecological disturbances. Like other kinds of invasive animals, non-native sliders compete with native turtles for habitat, basking spots, and food to the detriment of the naturally occurring species. An additional problem associated with the Red-eared Slider trade is the transmission of Salmonella bacteria In 2013 the CDC reported a Salmonella outbreak that affected almost 400 people in over three dozen states. Although domestic sale of turtles less than four inches in length was banned in 1975, eighty-nine percent of those affected by been exposed to small turtles (7). Several states, as well as the European Union, have banned turtle sales. Still, Red-eared Sliders are raised for export and a quick Google search indicates they can still be purchased via the Internet. Unless one is prepared for a decades long commitment, such a purchase seems ethically and environmentally unwise.
And so, on your next warm weather trip to GPFWA, keep an eye out for a large turtle with a greenish to olive-brown shell lounging about on a handy muskrat house. It is a scene far more pleasing than that of an aquarium-bound captive. Let your observation be a reminder that behind every animal one sees at GPFWA there likely lies a story of science, survival, or even history. Let it be a reminder that not only cranes and rails benefit from the Goose Pond restoration. There exist legions of other species equally at home and equally dependent upon the grand wetland which now graces southwestern Indiana.
1. Minton, Sherman A., Jr. Amphbians & Reptiles of Indiana. Ind. Acad. Sci. Indianapolis.