The fertilized female, or "sponge crab", produces approximately 2 million larvae in the salty waters near the mouth of the Chesapeake Bay. The tiny microscopic larvae, called a "zoea" (ZO-ee-ya) are swept out into the ocean where they go through a number of stages before they even resemble a crab. The whole surface of the body is enclosed in an external skeleton (exoskeleton) which the crab must shed in order to grow. This process is called "molting". The "zoea" molt into the next crab form, called a "megalops". This larvae, resembling a small lobster, migrates into the bay where it develops into an immature crab, or "first crab." Eggs hatched in late May or early June become immature crabs in about two months.

All crabs go into semi-hibernation during the winter, November to March. When the waters warm in spring, they crawl out and continue eating and molting. An immature female, or "she-crab", will molt a total of about eighteen to twenty-three times before reaching maturity. She will then cease to molt, after mating. Males have the same growth pattern, except that they do not cease growth after sexual maturity but continue to molt into the third summer. Since males continue to grow, a fully mature male crab will be larger in size than a mature female, called a "sook". Most female crabs attain full growth and mate only once, during their second summer.

Mating occurs from May through October in lower- and mid-Bay habitats where salinity preferences of the male and female overlap. The female is fertilized by the male during her last molt and only when she is soft (soft-shelled). During this period while the male is carrying the female, the pair is called a "doubler". The male stays with the fertilized female, or "sponge crab," protecting her from harm, until she is once again able to function as a hard-shell crab.

The fertilized eggs begin development internally and are later extruded out under the apron, producing a spongy, lemon-colored mass. As the embryonic crabs develop, the color of the egg mass darkens to orange, then brown, and finally black. Blue Crabs are serial spawners and release their larvae over a period of one or two weeks. Spawning occurs from May to September. Early reproductive females generally spawn prior to the coming winter, while those maturing later spawn the following spring.

One of the interesting characteristics of the blue crab is the way nature has allowed us to determine its sex. Blue claws mean the crab is a male, often called a "jimmy". Red tips on the claws mean it's female. Gender is also determined by the differences in the shape of the abdomen, or "apron", as it is commonly called. The male apron is T-shaped. In the young immature female, the apron is triangular and sealed to the body. However, in the mature female, this apron is broadly rounded (almost semi-circular) and free of the ventral (bottom) shell.

The next page offers photographic illustrations and other facts about the blue crab that will help you to identify the different aspects and stages in the life cycle of the blue crab.