Text says, The Blue Crab

illustration of male crab cradling a female crab

For a few days before and after her final molt, an immature female crab, called a "she-crab", is cradled by a mature male.  While the male crab is escorting the female crab, the two crabs are called a "doubler."

During the molt, the male lets go of the female, but remains nearby.

After molting, the male and female crab mate.

After mating, the two crabs resume the "doubler" (or coupling) position until the female's shell hardens.

Egg-bearing female crabs are called "sponge crabs."

When do Blue Crabs mate?

Blue crabs mate from May to October in the slightly salty waters of Chesapeake Bay.

graphic reads, Extra Credit

The sex of a blue crab is determined by the shape of the "apron".

Females have either a "V" shaped apron (immature)
or a very wide apron with a small tip (mature.)

immature female crab
An immature female blue crab, Callinectes sapidus. Sex and maturity determined by the "V"-shaped apron. 

mature female blue crab caught in a net
If the apron of a blue crab looks like the dome of the Capitol Building then it’s a mature female. The mature female has a very wide apron with a small tip.
The apron of a mature male blue crab
looks like the Washington Monument.

mature male crab caught in a net
 The male's abdomen is long and slender, resembling an inverted "T".

Photographs courtesy of Mary Hollinger, NODC biologist
NOAA - America's Coastlines Collection