More from my trip to Monomoy National Wildlife Refuge: I gathered these molts from baby horseshoe crabs that I found while walking on the beach.
A female horseshoe crab will lay 90,000 eggs or more during a spawning cycle. But only about 10 horseshoe crabs will make it to adulthood.
As larvae and hatchlings, juvenile and subadults, they will shed their shells or molt as they grow. Males are sexually mature after about 8 or 9 years and 16 molts. Females are not sexually mature until they are about 10 or 11 years old and have molted 17 times. Some horseshoe crabs continue to molt even after sexual maturity. No one knows how long horseshoe crabs live.
Source: National Park Service, U.S. Department of the Interior