Maryland Fish and Wildlife Conservation Office
Northeast Region



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Horseshoe Crab

Limulus polyphemus

Life Historyhorseshoe crab

  • During the high tides of the new and full moon in early spring, female horseshoe crabs emerge from muddy beds to begin a journey to shore to take part in their spawning ritual.
  • Females dig several nests to lay their eggs. The males, one-third the size of females, attach themselves to the rear of the female's carapace and are pulled over the nests to fertilize the eggs.
  • Horseshoe crabs attempt to protect their eggs by covering their nests with sand but often wind and waves shift the sand and leave many of the eggs exposed.
  • After molting several times, horseshoe crabs finally reach sexual maturity at between 9 and 11 years of age.


  • Until the 1990's, the harvest of horseshoe crabs was regulated by individual states. In 1998, an Interstate Fisheries Management Plan was adopted by the Atlantic States Marine Fisheries Commission (ASMFC).


  • Biologists from state and federal agencies participate in a Cooperative Tagging Program. Tag return data provides information about horseshoe crab migration patterns, distribution, abundance, and mortality, which informs the management of horseshoe crab populations.
  • State and federal agencies continue to work closely with researchers to conduct stock assessments, population modeling, and genetic analyses to better understand the status of horseshoe crab populations.
  • In 2001, a year-round, 1500 nautical-mile horseshoe crab reserve was established at the mouth of Delaware Bay.

Other Fish Facts

  • Horseshoe crab eggs are eaten by many migratory shorebirds which stop along the Atlantic coastline. Shorebirds almost double their weight from feeding on horseshoe crab eggs which gives them the energy source that enables them to continue their migration north. 
  • Horseshoe crabs are believed to have evolved during the Paleozoic Era (540-248 million years ago). Although it is called a crab, the species is more closely related to spiders and scorpions.
  • Horseshoe crabs are harvested commercially primarily as bait to catch whelk (conch), American eel, and sometimes catfish. In addition, pharmaceutical companies harvest horseshoe crabs to extract their blue, copper-based blood which contains a chemical substance, hemocyanin, which clots when exposed to bacteria. The blood is used to test drugs and medical equipment for the presence of harmful bacteria.

You can help by reporting any horseshoe crabs caught or found with our tag by calling the toll-free number printed on the tag 1-888-LIMULUS (546-8587) or by clicking the Horseshoe Crab Tag Form above. A certificate containing release information is awarded to those who report our horseshoe crab tags.


Last updated: February 18, 2016
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