Naturalist Fact: Blue Crab

Blue crabs (Callinectes sapidus) are a delicious resident of our island’s waters. They are members of the Order Decapoda, in which all members have ten legs. The blue crab has two legs modified as pinchers that aid in defense and feeding, six walking/climbing legs, and two legs that have adapted into a paddle shape that allow it to swim. These paddles are an excellent aid in mobility, as other species of crabs are restricted to the bottom or structures on which they can climb. Their common name comes from the bright blue color exhibited on the mature crab’s pinchers and legs, and their Latin name literally means “savory beautiful swimmer.”

Blue crabs are most abundant in our saltmarshes and tidal creeks in the late spring and summer months, and can be caught in traps, or simply by tying some bait to the end of a string, lowering it into the water, and waiting for the tug of a hungry crab. Blue crabs are omnivores, feeding on a variety of things including fish, oysters, snails, other crustaceans, and plant material. They will also scavenge the carcasses of dead marine life. Chicken is a popular bait when fishing for crabs.

As crabs grow, they periodically shed their exoskeleton, or molt. They separate from their shell and scoot out backwards, leaving the intact shell behind. Sometimes crabs will consume their molts for the calcium. The crab’s body expands (grows) while its shell is soft, and then will harden into a new exoskeleton. This process usually takes a few days. While they are in the state of “soft-shell,” the crab is very vulnerable and will take cover until their new shell has hardened.

Female blue crabs will only mate once during their lifetime and this happens after what is called the terminal molt. After the female sheds her shell for the last time and is still in the soft-shell stage, a male will mate with her and then guard her until she her new shell hardens. Later, the female will develop a spongy egg mass under the apron on her abdomen, which she will carry with her until the larvae hatch. Since females can only mate once, it is a common practice to release any females that are caught.

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