Reverence For The Horseshoe Crab: Museum of Natural History Helping To Preserve The Ancient Species

by Greg O'Brien

BREWSTER – The ancient horseshoe crab gives remarkable, almost supernatural, definition to staying power.

Ancient Horseshoe crabs predate dinosaurs, which first roamed the earth about 245 million years ago.

Tantamount to special effects in a Stephen King thriller, the body of a horseshoe crab, experts tell us, is divided into three parts that are joined together: a broad horseshoe-shaped “cephalothorax” (a connected head and thorax); a much smaller segmented abdomen; and a long, sharp tail-spine that at first glance, particularly among the young, can be menacing. The horseshoe crab also has no face!

Until recently, Horseshoe crabs, perilously declining over time, were considered by some the “Rodney Dangerfield” of marine animals.

“They got little respect,” says Maureen Ward, creator of the Cape Cod Museum of Natural History’s “Horseshoe Crab Head Start Program.” Among the first of its kind, it’s a public education and conservation program to preserve and protect horseshoe crabs, educate the public on horseshoe crab stages of life and their contributions to the environment, migratory birds, and human health. Ward works closely in the program with Tyan Bassett, museum animal care coordinator.

“We’ve had a high success rate,” Ward says.

Notes Cape Cod Museum of Natural History President and Executive Director Robert Dwyer, “Brewster’s Cape Cod Museum of Natural History has been deeply committed to the conservation of horseshoe crabs and protection of their critical habitats along the Massachusetts coastline. Horseshoe crabs are considered a ‘keystone species’ (a species upon which other species in an ecosystem largely depend). Their absence from the ecosystem can have devastating effects on other species.”

The museum’s Horseshoe Crab Head Start Program is available for viewing at the museum, where the public can observe the growth and development of horseshoe crab larvae in special tanks. The horseshoe crabs are carefully returned to the sea as they mature.

Here's how the program works.

In the spawning season from April 15 to June 7, Horseshoe crabs will bury their unfertilized eggs, a distinguished color of green, in six or eight inches of soft sand. In a natural instinct, male horseshoe crabs will then fertilize the eggs. Curiously, there is no direct female/male contact in this fertilizing process, other than at times male horseshoe crabs attaching to the backs of females until they lay their eggs, then the males slide off to fertilize the eggs.

Under the Horseshoe Crab Head Start Program, during spawning season, small amounts of horseshoe crab eggs are cautiously scooped up by museum personnel from a beach in Barnstable Harbor, Wing Island near the museum’s headquarters, Priscilla Beach in Orleans or other coastal areas. The eggs are gently put in museum tanks and monitored for health and growth. They are then released to waters near where they were spawned.

Locally, while the number of horseshoe crab eggs deposited annually on the flats of Cape Cod Bay and the Atlantic at low tide is impressive, the survival rate is a concern, given the pressures of nature, predators, commercial fishing industry harvesting, and biomedical research. While a female lays as many as 90,000 eggs each year, an estimated one in 10,000 will survive to adulthood, Ward says.

Adding pressure on the species, the harvesting of female Horseshoe crabs, as they make their way to the shoreline during spawning season, is a boon to the commercial fishing industry and to critical biomedical research. Horseshoe crabs are used as bait for eels and whelk (popular in Asia) and for critical biomedical research. Notes Smithsonian’s Conservation Biology Institute, “You may be alive today thanks to a horseshoe crab. Horseshoe crab blood contains a unique enzyme called Limulus Amebocyte Lysate, or LAL. It causes the blood to coagulate when exposed to bacterial endotoxins, which can be deadly. Biomedical companies use LAL to test medicines, vaccines, implants, and more for endotoxins. It’s how they ensure medical equipment is safe for people. Unfortunately, many horseshoe crabs die in the process of collecting their blood. Scientists are exploring synthetic alternatives to LAL. Finding a replacement will help ensure a future for horseshoe crabs and shorebirds.”

Help is now on the way in Massachusetts. According to the state Department of Fish and Game, new regulations are being promulgated: the harvesting of horseshoe crabs will be prohibited during the spawning season and limits will be placed on the number of horseshoe crabs to be taken before and after the spawning season.

That’s great news considering the past.

Says Ward, “For the most part in the 1950s, ‘60s and ’70s, you couldn’t get a fishing license unless you agreed that if you came across a horseshoe crab or a snail, you would kill it. At the time, both were conceived as competitors to a healthy shellfish industry.”

Yet the horseshoe crab continues to survive.

Notes the Florida Fish and Wildlife Conservation Commission, “There are four species of horseshoe crabs still around today. Only one species, Limulus polyphemus, is found in North America along the Atlantic and Gulf coasts from Maine to Mexico. The other three species are found in Southeast Asia. And despite existing for hundreds of millions of years, horseshoe crabs are nearly identical to their ancient relatives.”

There are many other significant and documented benefits to a healthy horseshoe crab population. Among them, horseshoe crabs till sand on the surface in shallow waters, akin to a farmer tilling the land, plowing up nutrients. Also smaller shellfish often hitch rides on the backs of horseshoe crabs, helping to create a more diverse, healthy ecosystem — sort of a marine Uber ride at no cost.

“The horseshoe crab is an evolutionary superstar,” adds Ward. “The species is an incredible story of survival and impact in so many ways, and teaches us not to take for granted the things we have determined to be insignificant in our limited knowledge. We don’t know what we don’t know.”

So here’s some of what we know, according to Smithsonian’s Conservation Biology Institute and other sources (

“Horseshoe crabs are not real crabs; they are arthropods and more closely related to spiders and scorpions.

“It takes two to four weeks for horseshoe crab eggs to hatch. Tiny crabs emerge, smaller than the eraser on a No. 2 pencil, and with nearly see-through shells. The baby horseshoe crabs find shallow, sheltered waters to live in. They molt (shed old shell, for new shell growth) several times in their first year, shedding their old shells to reveal new shells underneath. Their shells darken as they age. The crabs continue to molt, but with less frequency, as they grow older. (Horseshoe crabs can live for 20 years or more; female crabs are larger than male crabs, given size needed for carrying eggs; they molt an estimated 16 to 17 times over a period of nine to 11 years before maturity is reached.)

“Horseshoe crabs walk on 10 legs and use their last pair, called the chelicera, to move food into their mouths. They eat worms, algae, clams, and other small prey that they root out in the sediment on the ocean floor. Horseshoe crabs have no jaws, so they crush their meals between their legs before eating.

“A horseshoe crab’s pointed tail is not for self-defense. Horseshoe crabs are easily jostled by ocean currents and waves — and each other. When a crab gets stuck upside-down, it uses its tail, called a telson, to flip over. Horseshoe crabs can also use their telson as a rudder to help steer as they swim upside down.

“Many shorebirds can’t survive without horseshoe crabs. Thousands of shorebirds descend on the Delaware Bay in May to feast on horseshoe crab eggs. Red knots, ruddy turnstones and sanderlings and other species rely on the fat-and protein-packed eggs to power their long flights. For red knots, this important stopover is the last chance to fuel up before the final leg of an epic 9,300-mile migration from South America to the Arctic.”

And so in celebration and reverence of the horseshoe crab, the Cape Cod Museum of Natural History on June 19 is celebrating International Horseshoe Crab Day with various impressive presentations and demonstrations.

“Please join us!” says Dwyer.