Even though they live, as poet Ogden Nash put it, “twixt plated decks,” slider turtles (Trachemys scripta) mate as most familiar pets do: After courting a female, the male moves behind the female and inserts his penis into her cloaca. Sperm then swim up the female's reproductive tract, where they are held until ovulation. Shortly thereafter, the female deposits eggs in a terrestrial nest.
However, the unusual body plan of turtles has forced them to evolve a few unusual adaptations to their breeding behavior.
When temperatures start rising in the spring, male slider turtles begin chasing and courting females. Usually, courting males swim in front of the females and approach them head-on. Once in front of the females, the males begin stimulating the females’ faces with their long claws. When a female accepts a male’s advances, he swims behind her and attempts to mate. If the female is receptive, she will not protest the male’s advances, but if she is not receptive, she will swim away repeatedly.
The first step in the mating process is for the male to maneuver his tail – which is much longer than that of the female – underneath the female’s tail. Once he has accomplished this, he will try to grab the front of her shell with his long claws, to hold himself in place.
The male turtle carries his penis, when not in use, inside his cloaca -- the chamber, located inside the tail base of both males and females, from which the urinary, reproductive and digestive systems empty. Once the male aligns his cloaca with the female’s cloaca, he everts his penis and inserts it into the female’s cloaca. Mating usually lasts a few minutes, and then the animals go their separate ways.
While males and females may mate repeatedly over the course of days or weeks, the male will have no further involvement with the offspring after conception has taken place.
A few weeks after mating, females begin looking for a place to deposit their eggs. In the wild, they frequently select sand-covered shores with plenty of sun exposure; turtle-keepers must provide pets with a suitable egg-deposition site, or the turtles may become egg bound. Sliders require a large land area with a sand or sand-and-soil substrate in which to dig a nest and deposit their eggs. The land area must be at least two to three times the turtle’s length, and as deep as the turtle is long.
After laying her eggs, the female will have nothing more to do with the offspring.
Note that even virgin turtles can deposit eggs, so it is wise to maintain an egg-laying place in the cage at all times when keeping female slider turtles.