Because of its elusive behavior, many people never see the northern diamondback terrapin. The upper shell, known as the carapace, can be gray, black or brown and the bottom shell, the plastron, is yellow or olive and often mottled with dark blotches. The skin is pale or white with striking black flecks and lines that create a design unique to each individual terrapin, just like a person's fingerprint. Males are mature at about age 7, weigh about a pound and are about 4 inches along the plastron. Females mature at about 12 years, and can weigh up to 7 pounds and and reach a length of 9 inches.
Diamondbacks live in brackish and coastal waters and marshes.
Their webbed feet make them agile swimmers and sharp claws help them move about the marshes. They eat clams, snails, worms, crabs, insects and fishes. Diamondbacks usually mate in May, and always mate in the water, usually at night. Females can store sperm and produce fertilized eggs up to four years after mating. They lay their pinkish, leathery eggs in June and July in nests dug out of sandy beaches or marsh edges above the high tide line.