Crabs mate in the early summer and in the fall. It is important for crabs to mate when the female crab has recently molted and her outer shell is soft. If the female's shell is no longer soft, the crabs are unable to mate successfully. Before the female molts, she releases chemicals that attract male crabs to come and mate with her while there is still enough time.

Female crabs enter maturity by molting after attracting male crabs. These attracted male crabs often fight with one another in order to win over a female crab. As part of a mating ritual, the male crab stands on the tips of his legs and sways around from side to side. If he is accepted by a female who is about to molt, the male carries the female for several days until she is ready to molt.

After the outer shell has been shed, the two crabs mate. This process can take several hours and the females keep the males' sperm in a sac until they are ready to fertilize their eggs later on. The fertilization usually occurs during migration season. Sometimes, male crabs continue to carry and cradle female crabs after they have mated to ensure the female does not mate again while her new shell is still soft.