One way to learn more about blue crabs is to take a closer look at their anatomy.

On the outside: swimming legs and eyestalks...

The outside parts of a blue crab are hard. This is called their exoskeleton. Its back legs look like paddles and are called swimming legs. Crabs also have six walking legs and two claws. Using their swimming legs or walking legs, crabs can move pretty quickly to catch prey or to escape from predators. And those claws? If you've ever been pinched by these crustaceans, you would know what they use them for. When crabs are threatened, they extend their claws in a defensive posture.

You can also see two eyestalks protruding from the front part of the shell. These eyestalks can stick out so the crab can see in the front, back, and sides if need be. There are two sets of antennae. These are used by the crab to sense vibrations in the water and collect chemical clues for detecting predators and prey. Click on the image to see the crab move one of the sets of antennae.

Because the shell of a blue crab, the exoskeleton, is hard and doesn't grow, crabs must shed their shells in order to grow. This process is known as molting.

On the inside: gills, heart and stomach...

Inside the crab are the soft parts. Crabs, like all crustaceans, have gills to take up oxygen in the water. Crabs also have a stomach and a heart that pumps a liquid through the body to supply the tissues with oxygen. The many nooks and crannies in the crab contain the muscles that move the claws, walking legs, and swimming legs.

Male or female?

An easy way to tell the difference between an adult male and female crab is look at a crab's underside and examine the shape of its abdomen. By looking at the abdomen you can see the difference between adult males, adult females, and juvenile females.

The male has an abdomen (or apron) shaped like the Washington Monument.

The female has a rounded abdomen, shaped like a honey comb, or like the Capitol dome in Washington, D.C.

Immature female crabs have an abdomen that's more shaped like a triangle.