Blue crabs mate in early summer and fall. The crabs can only
mate when the female crab has just molted and her outer shell is
still soft. Female blue crabs, like the males, molt several
times in order to grow, but a particularly important molt when
an immature female becomes mature. Immature female crabs that
are ready to mature on the next molt are called pre-pubescent
females and release chemicals to attract mature male crabs in
the area. The male crabs may have to compete with each other for
the female. During a distinct mating ritual the male crab stands
on the tips of his walking legs and uses his swimming paddles to
rock from side to side. If the pre-pubescent female accepts the
male, the two "double-up" and the male carries her around--
usually for one or two days--underneath him until she is ready
to molt. When the female molts, they separate for a little
while, but immediately after she has molted and shed her old
outer shell, the crabs double-up again and begin to mate. The
photo below shows mating c