Each major estuary along the coast is believed to have a discrete horseshoe crab population that can be distinguished by adult size, carapace color, and eye pigmentation. Along the Atlantic coast, horseshoe crabs are most abundant between Virginia and New Jersey with Delaware Bay at the center of the species distribution. Horseshoe crabs molt or shed their shell to grow. Molting occurs several times during the first two to three years and about once a year afterwards. Molting occurs approximately 16 to 17 times over a period of 9 to 11 years before sexual maturity is reached and once mature, it is believed they no longer molt.
Females reach maturity one year later than males and consequently, go through an additional molt.
Mature horseshoe crabs then repeat what has occurred for years, an annual spring migration to inshore spawning areas. If a horseshoe crab can survive the rigors of spawning, it may live to 18 years of age. Horseshoe crabs are well known for their highly visible mating activities. Spawning in the Chesapeake usually begins in late May when large numbers of adults move onto beaches to mate and lay eggs. The peak in spawning activity usually coincides with the full moon and evening spring tides.