Male lobsters possess a pair of bony swimmerets close to the body, while females have only feathery swimmerets. The females also have a rectangular sperm receptacle on the underside of the tail, between the second pair of legs. Male lobsters generally grow larger claws, while females grow a wider tail.
Female and male lobsters each play a specific role in the mating ritual. Female lobsters grow more slowly, often going several years between molts. Just before molting, the female lobster identifies her preferred male, approaches his den and sends out a pheromone attractant. The male responds by meeting the female for a brief ritual dance, after which they return to the male's den, where the female molts and becomes ready to mate. During the mating process, the male passes his sperm to the female using his specialized swimmerets.
The female remains in the male's den until her new shell hardens, then she departs. She wanders for several months before laying her eggs and fertilizing them using the sperm stored in her sperm receptacle. She secretes a sticky substance that binds the eggs to her tail, where they will remain for nine to 11 months. During this time she cares for the eggs by fanning them with fresh, oxygenated water. When they are ready to hatch, she raises her tail and releases the eggs into the current.