Illinois Natural History Survey - University of Illinois

Spiny Softshell Turtle

Susan Post

 

While walking along the Cache River in southern Illinois this summer, I noticed a flattened boulder along the side of the stream. Using my binoculars I realized this wasn’t a rock but a large turtle, basking in the sun. Back at the car, I pulled out my Amphibians and Reptiles of Illinois and discovered I had seen a female spiny softshell turtle, Apalone spinifera—a new species for my Illinois reptile and amphibian life list and one that I wanted to learn more about.

Of Illinois’ 60 species of reptiles, perhaps the most highly adapted for an aquatic existence are the state’s two species of softshell turtles—smooth and spiny. The spiny softshell turtle occurs throughout the state in lakes, sloughs, mud-bottomed streams, and sand-bottomed rivers. It is most abundant in the latter. These turtles spend most of their time in well-oxygenated water either foraging, floating at the surface, or buried in the soft bottom with only their heads and necks protruding. The exceptional feature of any turtle is its shell, which is divided into two parts, carapace (the upper shell) and plastron (the bottom part of the shell). Both parts of the shell are made up of bones that are covered with a horny scalelike covering called scutes. Softshell turtles have an almost circular upper shell; instead of scutes, both their carapace and plastron are covered with soft and leathery skin. The carapace bends and the edges droop like a flap over the hole through which the head and neck are withdrawn in time of danger. When removed from the water, softshell turtles resemble gray pancakes and this has led to common names of flapjack or pancake turtles. Spiny softshell turtles are dull-olive in color with narrow yellow borders. They have numerous black rings scattered over their carapaces and spiny projections along their anterior edges. Their heads are olive with yellow, black-bordered stripes on each side of the head and neck extending through the eyes. Their limbs are olivespotted and marbled in black with paddlelike feet. Females are usually twice the size of the males. Carapace length can be 18 inches in females and 8.5 inches in males. They have long necks, narrow heads, and snouts that are slender proboscises. Their skin is three to four times more permeable to water than that of hardshell turtles. Thus, if kept out of water for two to three days, they may die of dehydration. Fleshy lips cover strong mandibles, hiding the fact that these turtles can bite with the force of snapping turtles. While these turtles may look like pancakes, they have long necks, cutting jaws, raking claws, and are capable of sudden movement. They run with great speed for a turtle and swim even faster. Spiny softshell turtles spend a lot of time basking on rocks, logs, or sandbanks. While basking they usually turn to face the water, ready to make a rapid escape. These turtles are impossible to stalk and once alarmed they are difficult to overtake. They usually bask alone, and not before 10:00 a.m. Spiny softshell turtles will bury themselves in the sand at the very margin of a stream; inconspicuous craters mark the sites where they are buried. They lie just deep enough for their long pointed snouts to reach the surface for air, like snorkels. However, they don’t have to get air from the surface. While the turtle is submerged, it pumps water in and out of its mouth and pharynx. The highly vascular lining of the pharynx removes oxygen from the water and expels carbon dioxide into it. From late October until late April or May, the turtles bury themselves in sand or mud and remain until temperatures warm. They will hibernate beneath the water in about two to four inches of substrate. Once mating occurs (late spring) the female will nest, laying her eggs in sand or soil, which is close to the water and in full sun. She will nest from mid-May until July and will lay an average of 18 spherical, brittle-shelled eggs. She can have up to four clutches of eggs per season. Hatchlings are in evidence by late August. Spiny softshell turtles are carnivorous, feeding on crayfish, fish, and aquatic insects. When feeding they crawl or swim along the bottom of the water in a random fashion, thrusting their snouts under stones into masses of aquatic vegetation. They will take prey from ambush and also actively pursue it. These turtles are not without their predators. Skunks and raccoons destroy their nests; fishes, snakes, wading birds, and other turtles eat the young. The biggest problem for adults is decapitation by fisherman after being hooked on their lines.

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