A snapping turtle takes a defensive posture

By Jeff Mitton
Two feisty creatures met on a lonely sandy road beside a lake in the Sand Hills of Nebraska.

I was going south, looking for painted turtles. The ponderous snapping turtle was going north, probably looking for the right spot to dig a hole in which to lay her eggs.

We were both a little surprised and a bit apprehensive.

She stopped and fixed me in her glare. She had already seen enough of me, but I approached for a better look. When I got within 20 feet, she gathered her front feet close to her head, kept her chin to the ground and propped up the rear of her shell by extending her back legs and using her tail as a support.

Her posture superficially resembled a dog's bow used to solicit play, but the signal could not have differed more. This was menacing, the defensive posture of a threatened animal perfectly capable of defending itself.

The posture reminded me of a sprinter coiled at a starting line, ready to lunge. Snapping turtles are fierce when they feel threatened and they are deceptively fast. An adult snapper has a long, flexible neck, powerful jaws and a sharp beak.

I have heard a reliable account of a snapper biting through a broomstick, so I was determined to keep my slow reactions and my soft, slender fingers at a safe distance.

Common snapping turtles, Chelydra serpentina, grow big. This one appeared to have a shell almost two feet long and I estimated that it weighed 25 to 30 pounds.

Overfed snappers kept in captivity grow longer and may exceed 70 pounds. Larger still are alligator snapping turtles, Macrochelys temminckii, which occur in the southern states and reach 175 pounds in the wild and well over 200 pounds in captivity.

The common snapping turtle would not be confused with other species. Its shell has low ridges extending from the front to the back of the shell and the upper edge of its long tail has a ridge of saw-toothed keels that remind me of the plates on the back of a stegosaurus, our state dinosaur. The legs are thick and powerful and the toenails are large. The legs and neck are covered with tubercles.

Snapping turtles are sit-and-wait predators with several unique adaptations. In shallow marshes, they bury themselves in the soft mud with only their heads exposed. Their long, flexible necks can reach up until only the tip of their snout reaches the surface. The nostrils, at the very end of the snout, serve as snorkels, allowing the turtle to breath occasionally without making a stir.

With its body buried in the mud and a fresh breath of air, a turtle lies on the bottom, opens its mouth and extends its tongue. The tip of the tongue has an appendage that can be wriggled like a worm to serve as a lure for fish. Powerful jaws grab hungry fish that come to take the worm.

If the substrate is firm or rocky so the turtles cannot bury themselves in mud, they are camouflaged by a dense growth of algae on the top of their shells.

Once I had gotten a good look, I was content to leave her to the important task of choosing a site for her eggs. Choice of nest site is especially important in snapping turtles because the gender of the offspring is not determined by genetics, but by the developing temperature of the buried eggs. If the eggs develop at 26 degrees Centigrade or cooler, more than 90 percent will be male. But if the eggs develop at 30 degrees Centigrade or warmer, all will be female.

Jeff Mitton (mitton@colorado.edu) is a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado. This column originally appeared in the Boulder Camera.

July 2011