Appearance

The blue crab's carapace (shell) varies in color from bluish to olive green, and can reach up to 9 inches across. The carapace has nine marginal teeth on each side; the ninth teeth are strong spines. Its claws are bright blue, and those on mature females feature red tips. Blue crabs have three pairs of walking legs and paddle-shaped rear swimming legs. Males have a strongly tapered abdomen, or "apron," that resembles an inverted T, mature females have a broad, rounded abdomen, and immature females have a triangular abdomen.

Feeding

Blue crabs will feed on nearly anything they can find, including clams, oysters, mussels, smaller crustaceans, freshly dead fish, and plant and animal detritus. They will even eat smaller and soft-shelled blue crabs.

Predators

Predators include large fish like croakers and red drum; fish-eating birds like great blue herons; and sea turtles.

Reproduction and Life Cycle

Blue crabs mate from May through October in the brackish waters of the middle Chesapeake Bay. Before mating, males cradle a soft-shelled female in their legs, carrying her for several days while he searches for a protected area for her final molt. Once she molts, the pair mates. After mating, the male continues to cradle the female until her shell hardens. Males eventually leave to search for another mate, while females migrate to the saltier waters of the lower Bay.

Females develop an external egg mass, or sponge, beneath their aprons. Each bright orange egg mass may contain between 750,000 and two million eggs. The egg mass darkens as the developing larvae consume the orange yolk. In about two weeks, larvae are released into the salty waters near the mouth of the Bay.

Currents transport blue crab larvae, called zoea, to the ocean, where they molt several times as they grow. Eventually, zoea return to the Bay and other estuaries. During their last larval molt, zoea metamorphose into a post-larval form called the megalops. Megalops crawl over the Bay’s bottom to reach the upper Bay and its rivers. Megalops eventually metamorphose into immature crabs, which look like tiny adults. Immature crabs molt several times before they reach maturity, about 12 to 18 months after hatching. Few blue crabs live longer than three years.

Did You Know?

• The blue crab’s scientific name comes from the Greek words for “beautiful” and “swimmer.”
• Male blue crabs are known as “jimmies,” while mature females are called "sooks."
• Blue crabs are one of the most important commercial and recreational catches in the Chesapeake Bay.
• For most of the last two decades, the total number of blue crabs in the Chesapeake Bay has lingered below the long-term average.

Sources and Additional Information

• Learn the Issues: Blue Crabs by Chesapeake Bay Program 
• Life in the Chesapeake Bay by Alice Jane Lippson and Robert L. Lippson
• Chesapeake Bay: Nature of the Estuary, A Field Guide by Christopher P. White
• Maryland Fish Facts: Blue Crab – Maryland Department of Natural Resources
• Animal Diversity Web: Callinectes sapidus – University of Michigan Museum of Zoology
• Callinectes sapidus – Smithsonian Marine Station at Fort Pierce