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. 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.
Most female crabs attain full growth and mate only once, during their second summer.
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.