The Life Cycle of a Fiddler Crab

Coastal mud flats come alive as fiddler crabs emerge from their holes each time the tide recedes. These tiny crustaceans live in burrows dug into the sand and mud and feed on the algae they find on the flats between tides. Each male crab has one large, fiddle-like claw that it uses to attract a mate and sometimes for fighting, and a smaller second claw for eating and fighting. The females’ claws are of equal size.

General Behavior

Fiddler crabs live in large colonies, often consisting of hundreds or even thousands of individuals. During periods of high tide, each crab scuttles into its hole and plugs the opening with mud. After the tide recedes, the fiddler comes out to search for food, scooping up sand and mud as it seeks algae and other bits of food. As it finishes each mouthful, the fiddlers discard pellets of sand and mud that end up piled along the shore until the next high tide washes them away.

Mating

The male fiddler crab digs a burrow in the shape of an “L” that is anywhere from 14 to 36 inches long. When it’s time to breed, he stands by the entrance to his hole, waving his large claw and stamping his feet to get attention. An interested female enters the male’s burrow and he follows her in, stopping to plug the opening before continuing down to mate with her. While most crabs can only mate right after molting, while the female's shell is soft, fiddlers crabs are unique because they don't need to wait and can breed anytime throughout the summer.

Larvae

After breeding, the female incubates her eggs for about two weeks and then releases them into the ocean. Some fiddler crabs can release eggs every two weeks as long as the weather remains warm. The eggs quickly hatch into free-swimming larval young that live at the surface of the water, along with other types of plankton. After a series of molts, the larvae grow and eventually enter the megalop stage, the last period before they complete their metamorphosis and become bottom-dwelling crabs.

Juveniles

Once the larval crabs are ready to complete their metamorphosis, they return to the marshy areas and transform into fully-formed juvenile crabs. These tiny creatures continue to molt as they grow, but fiddlers don’t discard their old shells, they absorb them. When the juveniles are big enough, they become sexually mature and go on to have their own young. Depending on the type of crab this can take anywhere from several weeks to several months. The fiddler crab’s lifespan is usually between one and two years.