The Mating Dance
For most crabs, mating season occurs during warmer weather, and if the crab makes its home in the ocean, the waters need to be a warm temperature as well. Other times during the year, crabs remain dormant or spend their time harboring eggs and releasing young that were created during mating season. When this time arrives, male crabs must find a female crab that has matured sexually and attract her. They do this by performing what equates to an elaborate mating dance. Usually, the male crab will rise onto the tips of his legs and move from side to side in front of the female. At the same time he will wave his claws in the air to attract her. This dance is not only done to grab the female's attention, it is also the time when the male sends out pheromones from glands under his claws into the air. These chemicals sexually attract females and get them ready for the mating ritual. The male will continue to do this until he finds a female who is ready and willing to mate.
A female will respond and let a male know that she is ready to mate by following suit and waving her claws in the air as well. A female is ready to mate when she is in the molting stage, which is the only time when her shell will be soft enough for mating. The interested female will turn around and back in towards the male, who then cradles the female underneath him with his legs. They will remain in this position, which goes by different names, depending on the crab, but is often called a doubler. The crabs remain this way until the female's shell is soft enough for mating to begin. In some species of crabs, this can last up to 1 week.
When she is ready to mate, the female will expose two triangle-shaped holes in her abdomen called gonopores. The male will then insert slender gonopods, which look like antennae, into the gonopores and transfer sperm this way. Once again, the time it takes for this stage of the mating process to complete depends on the crab, but averages around 5 hours. The female stores the sperm in special areas of her abdomen. They can be stored here indefinitely to create multiple egg sacs throughout the crab's life. When eggs are produced, they are carried underneath the female until they are ready to hatch, and when they do they are released in large groups whose numbers depend on the species of crab.