In cartoons, when a turtle is spooked, it retreats into and closes up its shell. While used for comic effect, this imagery is based in fact — although not all turtles are capable of this protective feat. In the Northeast, there are three native turtle species that have hinged shells: the Blanding’s turtle (Emydoidea blandingii), the common musk turtle (Sternotherus odoratus), and the eastern box turtle (Terrapene carolina carolina).
Turtles have a lower shell, called a plastron, and an upper shell, or carapace. In hard-shelled turtle species, the shells are made up of bony plates that are covered with scale-like “scutes”. The scutes are made of keratin, the same protein found in our fingernails and hair, and give turtle shells their color.
Hinged-shell turtles have a split in the plastron, just behind the turtle’s front legs. The plates along this hinge are connected by cartilage, and specialized joints allow these turtles to pull the plastron toward the carapace; some hinged-shell species can completely close their shells, while others can only partially close. While most turtles can retract their heads and limbs into their shells, being able to seal these body parts within is an effective defense against predation.
Several animals, from coyotes to otters, will eat turtles. “If you’re a fairly adept critter like a raccoon, you can pry out a leg and have a snack,” said Jim Andrews, coordinator of the Vermont Reptile and Amphibian Atlas. “It’s not at all un.