Atlantic Horseshoe Crab - Life Cycle and Behavior

Life Cycle and Behavior

The crabs feed on mollusks, annelid worms, other benthic invertebrates, and bits of fish. Lacking jaws, it grinds up the food with bristles on its legs and a gizzard that contains sand and gravel.

They spend the winters on the continental shelf and emerge at the shoreline in late spring to spawn, with the males arriving first. The smaller male grabs on to the back of a female with a "boxing glove" like structure on his front claws, often holding on for months at a time. Often several males will hold on to a single female. Females reach the beach at high tide. After the female has laid a batch of eggs in a nest at a depth of 15–20 cm in the sand, the male or males fertilize them with their sperm. Egg quantity is dependent on the female's body size and ranges from 15,000-64,000 eggs per female.

"Development begins when the first egg cover splits and new membrane, secreted by the embryo, forms a transparent spherical capsule" (Sturtevant). The larvae form and then swim for about five to seven days. After swimming they settle, and begin the first molt. This occurs approximately twenty days after the formation of the egg capsule. As young horseshoe crabs grow, they move to deeper waters, where molting continues. Before becoming sexually mature around age 9, they have to shed their shells some 17 times. Longevity is difficult to assess, but the average lifespan is thought to be 20–40 years.