Horseshoe Crab — CCE Marine Digital Education

The Horseshoe Crab

The horseshoe crab is often referred to as a “living fossil” – they came before the dinosaurs over 350 million years ago and they live among us today, unchanged. Horseshoe crabs are built like a tank and are masters of defense, with a strong domed carapace protecting them from above and a hard exoskeleton covering their bodies. Horseshoe crabs are arthropods but in their own class called Merostomata. Contrary to popular belief, they are not crustaceans (like true crabs, lobsters and shrimp) but rather more closely related to arachnids like spiders and scorpions.

Horseshoe crabs can be found all up and down the coastal eastern U.S. They often reside in enclosed areas, called estuaries, which are protected from the open ocean, but venture out to feed. They lay thousands of tiny eggs during the high tides of full and new moons in May and June. Once baby horseshoe crabs emerge, they spend the first two years of their life close to shore. Horseshoe crab eggs are an essential link in coastal food webs. They serve as a vital food source for migratory shore birds, turtles, and fish. These eggs are crucial to many of these shore birds completing their long migratory journeys, by providing them with energy along the way.

Horseshoe crab blood has become crucial in the medical and pharmaceutical fields. The chemical (LAL, Limulus Amoebocyte Lysate) in their blood can detect bacteria, so technicians often use this blood to ensure that medical products are clean and safe to use. Their blood contains copper which gives the blood a blue color.

Cornell Cooperative Extension works with citizen scientists who volunteer each spawning season to count and tag horseshoe crabs at various locations around Long Island. This monitoring program helps scientists and state agencies have a better understanding of the population size and how to better regulate this important commercial fishery. Visit nyhorshoecrab.org to see how you can help local horseshoe crab populations remain viable for generations to come!