Natural History Museum To Celebrate Horseshoe Crab Day

BREWSTER – You’d be hard pressed to find a more enthusiastic supporter of horseshoe crabs, outside of the world of arthropods, than Maureen Ward.

She’s the horseshoe crab majordomo at the Cape Cod Museum of Natural History and and will serve as a prime hostess along with 30 or so volunteers for the International Horseshoe Crab Day events at the museum on Friday, June 19 from 10 a.m. to 2 p.m. That’s when the museum celebrates the fifth annual holiday (which is actually June 20) with over a dozen learning stations, handouts, guest speaker shorebird specialist Liana DiNunzio of the Manomet Observatory in Plymouth and more.

“I’m a volunteer,” Ward said. “I started there a couple of years after I retired. I noticed people were not paying attention to horseshoe crabs the way they paid attention to other species. So I decided to learn about them. 

“They’ve been around 450 million years, since the dinosaurs. They have survived mass extinctions, extreme cold, extreme heat so I would say they’re the greatest of all time because they have survived. Very few animals have the evolutionary span of horseshoe crabs. If they did nothing else, that should put them in the Hall of Fame,” she said. 

Certainly they’d be the Babe Ruth, Ty Cobb and Honus Wagner of the animal kingdom.

“Ten years ago I started a program to raise horseshoe crabs for educational purposes and to hopefully inspire people to advocacy and stewardship,” Ward continued. “It was just after COVID. The International Union for the Conservation of Nature’s Species Survival Commission designated June 20 as International Horseshoe Crab Day. So I reached out to folks at the museum to see if there was some way to remember horseshoe crabs. The following year I was allowed to have a daylong celebration, and each year after I’ve built on that. This is my program, basically. I am the horseshoe crab geek and I refer to them as my horseshoe grandcrabs.”

Those would be the young crabs she raises from eggs. It should be noted that horseshoe crabs are not actually crabs. They have their own order in the arthropod phylum.

“I have a degree in biology and always worked in a hospital setting and I was always interested in science and nature, so it is a good fit for me being a volunteer,” Ward said. 

The exhibits highlight the resilience of horseshoe crabs, their importance to the marine environment and migrating shorebirds who eat the eggs, as well as the humans who harvest the horseshoe crab’s blue blood for use in medical testing. The blood, worth around $60,000 a gallon, contains hemocyanin, which gives the blood its blue pigment. Amebocyte cells in the blood clot when they come into contact with endotoxins from bacteria, so the Limulus Amebocyte Lysate test is used to test for the presence of bacteria on medical equipment such as pacemakers, vaccines, intravenous drugs and other surfaces or products that need to be sterile. 

Limulus polyphemus is the scientific name for the American horseshoe crab, which ranges from the northern east coast to the Gulf of Mexico. 

According to the Massachusetts Division of Marine Fisheries, 140,000 horseshoe crabs were harvested for bait in 2024 along with nearly 200,000 for biomedical testing. Nationally about 700,000 crabs were bled in 2021, according to the Atlantic States Marine Fisheries Commission supplying blood for 80 million tests. The crabs are returned to the sea but up to 30 percent might not survive. 

“Old timers tell you that there were so many horseshoe crabs (during breeding) you had to walk on top of them to get to the water. From the 1970s to the ‘90s there was an unregulated harvest and there was concern they were overharvested and that migratory birds were being impacted,” Ward said.

She noted two of the largest biomedical harvesters were on Cape Cod, in Harwich and Falmouth. 

“There continues to be a good market for bait,” Ward added. “It waned a bit last year because the population was in decline.”

Horseshoe crabs are used for bait for the eel and whelk fishery. The population decline led to limits on the harvest, such as those Massachusetts imposed: 140,000 for bait and 200,000 for biomedical per year. The harvesters have been hitting close to those limits.

“It’s been hard work to get more conservation measures such as not harvesting during spawning. That’s when they used to harvest them,” she said. “A year and a half ago the division of marine fisheries said not to do that anymore so inroads are being made. A bill is now looking at all the bait and biomedical harvest, but it would put a lot of stakeholders out of work.“

The 54-day harvest restriction is expiring as the spawning season is April 15 to June 7. The other bill Ward alluded to, H.5266, would end all harvesting by Jan. 1, 2029, terminating the bait harvest and pushing companies toward synthetic alternatives for the blood such as recombinant factor C. The bill was reported favorably out of committee on March 19.

“Horseshoe Crab Day is to take the fear out of what horseshoe crabs are and to teach how important it is to everyday life,” Ward explained. “A lot of what we know about vision comes from the horseshoe crab eye. The horseshoe crab has 10 eyes, including compound eyes and eyes on the tail so [visitors] will experience what a compound eye is and how you could benefit from extra eyes. They work with their eyes to regulate circadian rhythm and help the horseshoe crab tell the time to get up and the time to go to bed. Visitors will have an opportunity to feed horseshoe crabs at the aquarium and to see how tiny the juvenile crabs are.”

The 24 stations include a fossil exhibit, what horseshoe crabs eat and what eats them, the horseshoe crabs’ super power (their blue blood), their anatomy, molts and exoskeletons, their connection to the space program (their blood is used to test for antiseptic surfaces), live crabs in pools, their importance to migratory birds and much more. 

“Suni Williams of Needham was the first astronaut to use the horseshoe crab test in space,” Ward pointed out. “Nothing goes up to space that isn’t tested for bacteria. 

“Birds depend on horseshoe crab eggs for migration (as fuel and energy) when they stop in Delaware Bay or on Monomoy,” Ward continued. “We have live tanks with juveniles 3 to 5 years old and two adult crabs in tanks for that day. We’ll look at male and female body parts and talk about fossils.”

The horseshoe crab is a living fossil, but there are also actual fossils in the exhibit.

Ward also started the aquaculture program at the museum to raise horseshoe crabs.

“I go to the beach when they’re spawning and look for certain depressions and formations that tell me male and females were there, find the nest and eight inches in the sand I will find green eggs in clusters. The female employs a sticky substance and the sperm and sand sticks to the eggs and she covers it up and moves away. One female can lay up to 90,000 eggs. Only eight make it to adulthood because everybody is eating horseshoe crab eggs,”

A horseshoe crab will molt 16 to 17 times on the way to maturity, which takes 9 to 10 years.

“I collect the eggs with sand because a horseshoe crab has fidelity to the beach, it nests in the same location year in, year out. We use Instant Ocean (to keep them in tanks) and leave them in water with a warm temperature. In two to four weeks you can see the horseshoe crabs spinning in the eggs. They molt four times in the egg then emerge and swim into the water and settle in the sand.”

They have no tails initially and in 30 days have their first molt outside the egg.

“At that point they can take food and we feed them ground up shrimp. When they are three to four years old we add fish. We don’t keep them too long, about six years. They will molt for us so long as they are comfortable and the tank has a clean substrate.” After that they‘re brought back to the beach.

“People don’t see them when they’re that little, so it is fun for them,” said Ward. “The kids can see how small they are and see them scurrying across the sand. If we can make dinosaurs cuddly we can make horseshoe crabs approachable. No other animal has more impact on human health or wellbeing. They touch everybody in everyday life and provide food for many animals.”