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Publication #WEC182

The Horseshoe Crab1

Jami McLaughlin, Frans Lanting, David Griffis, Martin Main2

The American horseshoe crab (Limulus polyphemus) ranges from northern Maine to the Yucatan peninsula in Mexico, including Florida coastal waters. Horseshoe crabs are not actually crabs, but more closely are related to spiders and ancient trilobites that existed millions of years ago.

The horseshoe crab is not dangerous!

The horseshoe crab will not bite or sting you. In fact, it may save your life!

Sometimes this gentle animal needs a helping hand to survive!

Horseshoe crabs Are Important to the Marine Ecosystem

  • At least 11 species of migratory birds use horseshoe crab eggs as their primary food supply during northern migration.

  • Sea turtles, fish, crabs, and other marine species also feed on horseshoe crabs and/or their eggs and larvae.

  • Horseshoe crabs disturb and aerate the sea floor with plow-like feeding behavior, enhancing species diversity and abundance.

When Are We Most Likely to Encounter Horseshoe Crabs on the Beach?

  • Horseshoe crab adults move into coastal areas to mate during spring and summer, especially when the moon is full or in new phases. They prefer sandy beaches within bays and coves that are protected from wave energy.

  • Horseshoe crabs molt and shed their shells as they grow in size, and molts (cast-off shells) may be found along the beach and in tidal flats.

Horseshoe Crabs Help Save and Improve Human Lives

  • If you have ever received an injection or undergone surgery, horseshoe crabs have helped you.

  • Horseshoe crabs have blue, copper-based blood that contains a special clotting agent called LAL (Limulus Amebocyte Lysate). LAL clots when exposed to endotoxins, which are chemical poisons released by certain infectious bacteria. The FDA requires an LAL test on all human and animal injectable and intravenous drugs, on the medical devices used to deliver these injectable drugs, and on all prosthetic devices (such as hip replacements or heart valves).

  • Researchers have discovered important principles about the functions of human eyes by studying horseshoe crab eyes and optic nerves.

  • Chitin, a cellulose-like component from the shell of the horseshoe crab, is used to make chitin-coated sutures and wound dressings for burn victims. The chitin-coated sutures reduce healing time by 35% to 50%.

How You Can Help

  • If you find a horseshoe crab stranded upside-down, gently flip it over (by its shell) so it can use its legs to return to the water.

  • If you observe horseshoe crabs mating in Florida, please report the location and date to the Florida Fish and Wildlife Commission (call toll-free 1-866-252-9326, or e-mail

  • Please also report your sighting to ERDG at

To learn more about horseshoe crabs



This document is WEC182, one of a series of the Wildlife Ecology and Conservation Department, UF/IFAS Extension. Original publication date September 2004. Revised August 2015. Visit the EDIS website at


Jami McLaughlin and Frans Lanting, graduates of the Florida Master Naturalist Program (FMNP) Coastal Systems Module; David Griffis, county Extension director and Extension agent II, UF/IFAS Extenison Volusia County; and Martin B. Main, assocaite dean of Extension; UF/IFAS Extension, Gainesville, FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.