Horseshoe Crab -Not A Crab At All

by Tom Fucigna, Sr.

 
Don't crush them with stones - just flip them.

 
These marvelous creatures are not crustaceans more closely related to spiders. They date back to before the dinosaurs and are one of the oldest creatures on earth --- here 350 to 400 millions years. Only 4 species remain in the world. The North American species, Limulus polyphemus, only lives along the Atlantic coast from Maine to the Gulf of Mexico. The other three live along the southeastern shore of Asia.

 
And right here in Douglaston they have been coming onto the beach in late May/early June in a ritual that has gone on for time eternal. At the time of the full moon the female horseshoe crab comes ashore with anywhere from one to 5 or 6 male crabs attached to her or following. She lays up to10,000eggs in the sand. They are then fertilized by the males and all crabs return to the water. The female may return up to 8 times to lay more eggs. One out of 130,000 eggs will survive.

Some eggs will be eaten on the beach by migrating birds and some by gulls. Then, in 3 to 4 weeks when the hatched small crabs that survive the beach make it to the water, they become prey to the various predators in the sea.

 
Those that do survive will mature in 9-10 years and continue the cycle of breeding that has gone on forever. It is estimated that the adults will live seventeen to twenty-seven years.

 
Once the mating season is over you will notice what appear to be many dead horseshoe crabs on the beach. While a few may in fact be dead, the majority of what you see are molts or sheds of living crabs. The horseshoe crab has a hard shell on the outside (the exoskeleton) and a soft body inside. While the inner body grows, the outer shell does not. Therefore, the body extracts itself from the small shell and grows a new larger one. This process can go on sixteen or seventeen times until the crab reaches an age of 16 to 17 years.

 
Horseshoe crabs spend most of their time in bays and the ocean where they have few enemies. Their main enemies are gulls and people, and they are at greatest peril from both f these when they come ashore in the spring. The gulls will try to flip them over or take advantage of a crab that has been flipped over by the tidal movements. They will peck at the underside and eat the soft body. People will try to kill the crabs thinking they are dangerous. Although they may look grotesque to some, they are harmless and they feed on worms, mollusks, and other small animals that are found in the sea.

 
People also harvest the crabs for bait to catch lobster and eels. The government is currently concerned about over-harvesting the crabs for this purpose and there are groups being formed to monitor the process and make certain that the horseshoe crab is not bound for extinction.

If you get a chance to examine a horseshoe crab look first at the top side shell. You will discover two sets of eyes-one simple and located forward, and one compound about 1/3 of the way up the shell. Their eyes are more sensitive at night and can see three feet away. They have been studied in the past to help in learning about the mechanics of human vision. Their copper-based blue blood is used in biotechnology in many ways: testing injectable drugs and medical devices for the presence of endotoxins, in cancer research, and as an indicator of spinal meningitis.

 
If you look at the underside of the horseshoe crab you will see five pairs of legs. The first four pairs are for walking and the fourth pair for pushing along the sea bottom. Located behind the legs are the gills lined up like pages and therefore called book gills. The crabs can swim upside down using the gills to propel them.

 
The tail, which many wrongly think is menacing, is used as a rudder as the crab moves through the sand on the sea bottom. And should the crab be flipped over the tail is stuck in the sand to right the crab. It is an essential appendage and since it is attached by muscle it can break off. Therefore never pick up a horseshoe crab by the tail. For once it is gone it will never grow back.

 
Having learned a bit about these gentle creatures you can help make a difference- .Tell a friend, teach a child or family member and encourage all to respect this remarkable species.