• Miles of uncrowded white sandy beaches extend to the horizon, separating the clear blue ocean and undulating grass-covered dunes.

    Fire Island

    National Seashore New York

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  • Pet Restrictions in Effect March 15 through Labor Day

    Dogs/other pets (except for service animals) are not allowed in the wilderness or on any of Fire Island's federally owned oceanfront beaches from March 15 through Labor Day to help protect threatened and endangered beach-nesting shorebirds. More »

  • Backcountry Camping Permit and Access Procedures

    Reservations for required permits must be obtained through www.recreation.gov. Due to the breach at Old Inlet, access to both east and west wilderness camping zones must now be from Watch Hill or points west, and involve a 1½ to 8 mile hike. More »

  • Attention Watch Hill Ferry Passengers

    Due to channel conditions, delay or cancellation of ferry service between Patchogue and Watch Hill may occur. For updated ferry schedule information, please call 631-475-1665.

Natural History of Horseshoe Crabs

A close-up look at the underside of a horseshoe crab reveals the creature's mouth, appendages, and gills.
A close-up look at the underside of a horseshoe crab reveals the creature's mouth, appendages and gills.
 

Horseshoe Crab Biology

As adults, horseshoe crabs live in deeper water and come to shore to mate and lay eggs. Peak spawning occurs in New York in May and June, particularly during the evening high tides of new and full moons. After at least two weeks and up to several months later, the eggs hatch. These baby horseshoe crabs look just like an adult except that they do not have a tail and their eyes and digestive system are not yet fully developed. And they are small - only 3 mm across.

The young crabs will spend the next 3 weeks in the water. When they come back to shore they will be about 1/4 of an inch wide and have a tail and functioning eyes and digestive system. These juvenile crabs will stay close to shore for about 2 years before they move into deeper water. As larvae and hatchlings, juveniles and subadults, they will shed their shells (molt) as they grow.

Males are sexually mature after about 8 or 9 years or 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.

 
Horseshoe crab eggs on the bay shoreline

During a spawning cycle female horseshoe crab will lay 90,000 tiny eggs - about 4,000 eggs would fill a heaping teaspoon. From so many eggs it is estimated that only about 10 horseshoe crabs will make it to adulthood.

Many migratory shorebirds including the red knot, ruddy turnstone and sandpiper rely upon the energy-rich horseshoe crab eggs for food on spring migration. Horseshoe crab eggs and larvae are an important food for many fish (American eel, killifish, summer flounder, winter flounder).

 

Horseshoe crabs play an important role in the safety of many medicines used by people. Horseshoe crab blood cells (amoebocytes) attach to dangerous toxins produced by some types of bacteria (gram negative). When a crab is injured, the amoebocytes move to the wound and form a gel that surrounds and destroys the bacteria thus preventing an infection. Horseshoe crab amoebocytes are used to test intravenous drugs and vaccinations to make sure that they are free from gram negative bacteria. Horseshoe crab amoebocytes are also used to diagnose spinal meningitis and other human diseases. Horseshoe crabs are collected, taken to a laboratory where the blood is collected, and then released back into the environment. Within the boundaries of Fire Island National Seashore however the harvest of horseshoe crabs is not permitted.

Study of the horseshoe crab eye has taught scientists and doctors much of what we know today about the human eye.

Native Americans used and taught early settlers to use the horseshoe crab as a fertilizer for crops. Native Americans also ate horseshoe crab meat, used the shell to bail water, and used the tail as a spear tip. In the United States, horseshoe crabs continued to be used as fertilizer through the 1960s.

Horseshoe crabs are used as bait for catching eels and whelk.

 
 
 
 
 
 
 

Did You Know?

Piping plover on beach.

The piping plover is a federally threatened and New York State endangered species. It may be delisted when a total of 575 breeding pairs can be maintained in New York and New Jersey for five years. Fire Island National Seashore is currently the home of 15 - 20 nesting pairs of these shorebirds. More...