Campus Biodiversity: Red-Eared Sliders

They’re out. Stacks of them. Sometimes piled on top of each other like bricks, feet extended, much to the delight of students and visitors to the UT turtle pond. These campus charmers are turtles commonly known as “red-eared sliders,” or Trachemys scripta elegans.

The “red” comes from the red stripe behind their eyes. What about “slider?” This isn’t because they kind of resemble those tiny trendy hamburgers, but because they “slide” off logs or rocks into water when they are startled. They used to be called “Troost’s turtle,” in honor of American-Dutch herpetologist Gerard Troost (1776-1850).

Their native habitat covers the midwestern states, as far south as northeastern Mexico, into eastern New Mexico, and then Virginia in the east. However, due to their extreme popularity as pets, they can actually be observed in every continent except Antarctica. They’ve become such a problem that they have been deemed an invasive species by many countries and US states.

How did these turtles almost take over the planet? Well-meaning but irresponsible pet owners. In the 1900s, red-eared sliders were captured in the wild to be sold in dime stores and markets. They were small, cheap, cute, and became popular pets. By the 1950s, millions of red-eared sliders were being farmed and shipped for the pet trade, both here and abroad.

Enter Leonardo, Michelangelo, Donatello and Raphael. No, not the Italian Renaissance artists, but characters from the widely-popular comic book and movie franchise known as Teenage Mutant Ninja Turtles. These four sewer-dwelling New York reptiles battling evil with ninjustu are actually red-eared sliders, according to the second volume of the comics, and the 1990 and 2014 films. This pop culture representation caused a surge in popularity of the turtle as a pet.

But what is a parent to do when their child outgrows the turtle, or find out turtles aren’t soft and cuddly like Snowball or Spot? The local lake or park pond might seem like a good alternative to euthanizing the pet, but this well-intended relocation has had unintended consequences. As an invasive species, red-eared sliders can outcompete native turtles for food, nesting, and basking sites. They are typically larger, more aggressive, and produce more offspring. They also can carry diseases which can wipe out native populations.

In the state of Texas, red-eared sliders are native, however, and exist through most of the state with the exception of the west.  

LIFE CYCLE

After mating, a female turtle will wander from the pond or shallow lake to find a suitable place to lay her eggs. Using her hind legs, she’ll dig a hole and lay eggs there that will incubate from anywhere from 59-112 days. It’s during this time the sex of the turtles-to-be is determined. Only males are produced when incubating temperatures are between 72 to 81 degrees Fahrenheit. Females develop at warmer temperatures.

The new turtle uses an “egg-tooth” to break from its egg, but may stay inside its egg shell for a few days, living on nutrients provided by the yolk sac that will eventually be absorbed by the young turtle. About 21 days after hatching, the turtle will enter the water for the first time.

Young turtles of both sexes look the same, but as they reach sexual maturity, they will look different. Females are typically larger, with the carapace (the upper portion of a turtle’s shell) reaching up to 12 inches in length. The plastron (bottom shell portion) on females is flat, and for males it is somewhat concave.

Males have longer tails and longer claws on their front feet, claws which they make use of during mating which happens underwater. Claws allow them to hold on to the female. They also wave them around the female’s head during courtship, the thought being that this moves pheromones in her direction. If the female turtle is not into her suitor, she might get aggressive and send him on his way. However, if she’s into him, she will sink to the bottom of the water for mating.

A female can lay up to five clutches of eggs in a year, and each clutch can have between 2-30 eggs. Females don’t actually fertilize their eggs until they lay them, and since the sperm can remain viable in her body for some time, the female can lay and fertilize eggs in the following season.

The shell of a red-eared slider is made of its ribs joined together, then covered with a thin skin layer. Each rib is made of “scutes,” puzzle-like pieces that grow at their edges. This allows the shell to expand as the turtle grows.

Despite “ear” being part of its common name, these turtles don’t have a visible outer ear and their hearing is not so great. But the middle ear they do have is covered by a cartilaginous tympanic disc, which makes it a bit like a drum, and makes these turtles sensitive to vibrations. One can only wonder what a bus load of excited school children visiting UT’s turtle pond must sound like to them.

Red-eared sliders can live between 20-30 years on average. In captivity, however, their lives are much shorter.

UT'S TURTLES

During these summer months, you are bound to see the turtles out at the pond, basking in the sun. This is because red-eared sliders are cold-blooded poikilotherms, meaning they cannot regulate their body temperatures on their own. Sunbathing helps warm them, and if there aren’t enough logs or rocks to go around, they will stack themselves on top of each other. And what about that lovely arabesque pose some make, sometimes on top of a fellow turtle? That’s all about temperature regulation too, as outstretched limbs allow more effective heat absorption.

During colder months of which they aren’t many in Austin, turtles do not hibernate, but brumate. Turtles will stay at the bottom of the pond where temperatures are a little warmer. They enter a state of stupor, don’t eat, don’t defecate. Their breathing frequency lessens and they remain motionless. If temperatures rise a bit, the turtles will exit this cold weather state to bask in the sun, but will then return to their brumation state when it gets chilly again.

With winter a long ways a way for Austin, expect to see our beloved red-eared sliders soaking in the rays for months to come.