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CHATHAM — At 2 a.m., the Monomoy National Wildlife Refuge is shrouded in darkness, save for the headlamps of the two volunteers trudging through the dusky sand. Their mission is simple: count the horseshoe crabs who have gathered at the shoreline to spawn.
Drawn in by the light, a lone crab, the size of a dinner plate, scuttles up and lingers by the volunteers’ boots.
“I didn’t expect them to be so friendly and gentle,” one volunteer said. “They’re like sea Roombas.”
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Each year, dozens of volunteers descend on Southeastern Massachusetts’ beaches to survey the horseshoe crabs during their mating season, over the full and new moons in May and June. The surveys began as a way to keep tabs on the species’ adult population, but in recent years, they have taken on new significance.
Horseshoe crab blood is a premier ingredient in vaccine development. That puts the state’s biomedical industry and conservationist groups at odds. Amid increased scrutiny from both sides, the Massachusetts Division of Marine Fisheries is restructuring three full-time roles to focus more on monitoring the ancient moonlighting crab.
One of those positions will go to John Clark, now a part-time employee who conducts the horseshoe crab surveys at Swifts Beach in Wareham. This is the first year that the Town of Wareham has stopped beachraking on Swifts Beach, a practice that state regulators say may have inadvertently decimated the local crab population. Swifts Beach is the only beach surveyed in Massachusetts that has not seen an increase in horseshoe crabs over the past decade; in fact, it has seen a consistent decline.
On a warm Friday morning two days before the Strawberry Moon, Clark counts exactly zero horseshoe crabs on Swifts Beach. This is unusual, he said.
“Anecdotally, we have seen a lot more horseshoe crabs this year,” Clark said.
Blood money
The horseshoe crab is technically not a crab, but an arthropod related to a spider, tick, or scorpion. Their carapace resembles a leather rugby helmet, and their underside reveals eight legs and a set of gills. The only way to tell a female crab from a male, besides the female being larger, is the shape of the animal’s two front legs: males have a hooked claw to better cling to females during mating.
But it’s the inside of the horseshoe crab that matters most to some.
Bright blue and curiously milky, horseshoe crab blood contains a specialized protein that is critical to testing intravenous drugs and vaccines. The protein, called limulus amebocyte lysate (LAL), clots upon contact with certain bacterial toxins. That makes it an ideal substance for testing the safety and efficacy of anything doctors might need to shoot into your veins.
Massachusetts’ first horseshoe crab biomedical firm opened in 1974, using research out of Woods Hole to develop best practices around horseshoe bleeding. In Massachusetts, horseshoe crabs are harvested from the open ocean to be bled. Several rules aim to keep horseshoe crabs healthy during the bleeding process, such as limiting the time they spend out of the water and tagging bled crabs so the same crab doesn’t get harvested more than once a year.
Since the 1970s, the Division of Marine Fisheries has conducted studies on how horseshoe crab bleeding affects the population’s overall health. One state study, more than 20 years old, found that nearly 1 in 3 bled horseshoe crabs die prematurely.
But the truth is more complicated, DMF senior biologist Derek Perry said. The state is working on an updated study to determine the mortality rate of horseshoe crab bleeding, but studies done consistent with state regulations show a mortality rate between zero and 1%, Perry said.
As the state’s conservation priorities evolve, Perry has seen his work follow. When Perry started working for the state 23 years ago, horseshoe crabs made up just a quarter of his job, he said.
“Now it’s most of my job,” Perry said.
After a second biomedical firm opened in Massachusetts in 2022, Perry’s work expanded, as did cries from conservation groups to further regulate biomedical bleeding. This year, DMF is restructuring to create three new roles that focus primarily on horseshoe crabs.
Part of that work comes from the increased monitoring that comes with more horseshoe crab bleeding, Perry said.
“But it’s also based on the amount of misinformation that’s out there,” Perry said. “We’re trying to provide the public with more information.”
One of the ways the state has sought to conserve horseshoe crabs is through the Rent-A-Crab program.
Through the Rent-A-Crab program, some bled horseshoe crabs are then used for bait. Although the biomedical industry gets a lot of heat, it’s long been legal to use horseshoe crabs as bait to catch conch — also known as channeled whelk. In Massachusetts, 140,000 horseshoe crabs can be used for bait each year, whereas the biomedical industry can bleed up to 200,000 horseshoe crabs per year. These numbers are based on semi-annual trawl surveys of adult and juvenile horseshoe crabs.
The mortality rate for horseshoe crabs used as bait is 100%, Perry added.
Some states including New York have halted horseshoe crab bait landings altogether. Researchers are also looking into developing a synthetic form of horseshoe crab blood to use in vaccine and drug testing.
In 2024, activists successfully pushed to ban horseshoe crab harvests during the May-June spawning season. In 2025, some also backed H.B. 898, a bill that would have ended the horseshoe crab bait fishery in Massachusetts. A new draft of the bill currently sits in committee.
“This practice is unnecessary and unsustainable, especially given the availability of alternative bait sources such as the invasive green crab, which are abundant in our waters and negatively impacting the shellfish industry,” Chris Merl, the chairman of the Wellfleet Shellfish Advisory Committee, wrote in a letter to state lawmakers.
Another alternative to bleeding live horseshoe crabs is being explored at the Bristol County Agricultural High School in Dighton: horseshoe crab husbandry. This fall, environmental engineering students will attempt to care for and breed horseshoe crabs in captivity during their early life stages when they’re most vulnerable to predators.
Under the moonlight
On the far end of the Cape at Monomoy National Wildlife Refuge, it’s illegal year-round to hunt horseshoe crabs to use for blood or bait. That’s because at the peak of the May-June spawning season, the dynamic beach system can host hundreds of horseshoes looking for love.
Horseshoe crabs have 10 “eyes,” or ultraviolet light sensors, on the tops of their shells, which they use to tell night from day, full moon from new moon. They use these sensors to guide them to shore to spawn, burying their eggs in the sand.
Much like human dating, horseshoe crab spawning is a numbers game. Female horseshoe crabs can lay over 100,000 eggs in a season. Just six out of every 10,000 eggs will hatch, and even fewer will survive past the larval stage. It takes nine to 10 years for horseshoe crabs to reach maturity.
With those kinds of odds, it’s perhaps nothing short of a miracle that horseshoe crabs have existed for hundreds of millions of years, with ancestors tracing back 445 million years — more than 245 million years before the dinosaurs. The U.S. horseshoe crab population reached historic lows in the late 1980s and early 1990s, but is recovering thanks in part to renewed conservational efforts.
But Swifts Beach, for years, has hosted fewer and fewer horseshoe crabs, likely due to beachraking. It’s common on tourist beaches to drive a tractor with a rake attached over the sand to clear out seaweed and larger debris. But the raking typically takes place above the wrack line, away from where horseshoe crabs gather. This was apparently not the case in Wareham and other neighboring towns.
It took years for Perry and his team to find the responsible party, he said, but the beachraking below the high tide line at Swifts Beach stopped this year, Perry said. The Wareham Natural Resources Department did not respond to two requests for comment.
Swifts Beach is the only surveyed horseshoe crab mating spot on Buzzards Bay. Although some volunteers have seen an increase in crabs this spring, Perry said it will take another decade to know for sure if the horseshoe crab population rebounds in the bay.
But elsewhere in Massachusetts, horseshoe crabs seem to be thriving. This past season at Stage Harbor in Chatham, surveyors broke the record for the most horseshoe crabs counted in a single quadrat or 25-square-meter survey area, with 125 crabs in one quadrat. In 2024, the same beach broke the record for the most horseshoe crabs recorded in a single survey at 1,112 crabs.
In the middle of the night in mid-June, only about a dozen horseshoe crabs hug the shoreline at Stage Harbor. Some pairs are latched firmly together, scuttling under the knee-deep water in unison. Others wait in the grasses, unsuccessfully cold-approaching the other couples.
When asked why horseshoe crabs might spark such strong emotions in the public, Perry said it had to do with the species touching so many different perspectives.
“A lot of their life history plays out right in front of you,” Perry said. “You see these large spawn events in the spring — everyone sees them and kind of identifies with them.”
Email Brooke Kushwaha at bkushwaha@newbedfordlight.org.
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The restoration and protective regulations for the taking of horseshoe crabs has personal meaning for me. I wholeheartedly support more limited takings and restrictions to prevent any takings during the breeding and spawning seasons, from April 15 to June 7. As a child living on
the South Shore of Massachusetts, I recall our family outings to Duxbury beach. In the summer, I cherished the sight of numbers of horseshoe crabs moving slowly in the shallows of the bay. This peaked my curiosity and my interests in nature and biodiversity from childhood to maturity. Science has shown that exposure to nature as a child increases empathy for all living
species. As a child, seeing horseshoe crabs living unfettered in the bay was a both a blessing and a revelation. Today, I know that horseshoe crabs are part of a cycle of life that extends across the globe with the winged migration of shorebirds, including the federally protected red knot, who relies on the nutritious eggs of the horseshoe crabs as food and fuel for their herculean 9,000 mile migration from the tip of South America to the Arctic. This symbiotic relationship is jeopardized by Massachusetts’ slow recognition of the need to protect the embattled horseshoe crabs for future generations of children to experience.
Prehistoric horseshoe crabs are relatively unchanged over millennial time. They have perfected a form and function to have survived since the days of the dinosaurs. Can they survive the Anthropocene Epoch of over-harvesting, habitat destruction, and encroachment? Imagine my dismay, when I returned to Duxbury Bay in the summer as an adult to see a pick up truck, filled with horseshoe crabs piled on top of one another, parked in the sun by Duxbury Bay, now stripped of horseshoe crabs. My dismay turns to anger that the taking of horseshoe crabs has not been adequately regulated to date in Massachusetts. This must change, now. I am asking you to support the revised regulations on the taking of horseshoe crabs from Massachusetts’ waters. These conservative regulations are long overdue.
Wonderful story on horseshoe crabs! Thank you for covering it so comprehensively and charmingly, Brooke!
Very informative and a good read, it’s always great to see other towns and cities taking care of their coastal water ways and beaches. In New Bedford you can go to any of our beaches on our peninsula and you will see a lot of horseshoe crabs in our waters, but the sad part is for over 30 years these resources (Crabs, Conch, Quahogs, Etc.) have not been available due to all our local waters being closed due to pollution, see the link below (the New Bedford Area is the big blotch in red).
https://buzzardsbay.org/enjoy-buzzards-bay/shellfish/shellfish_closures_buzzards_bay/
Great comment Jeff, unlike Albert you include a link!
I only hope that when this horseshoe blood is used it’s marked as shellfish. After covid my husband now has a severe shellfish allergy. Let’s hope it comes with a warning!
As did the seal population, the horseshoe crab has migrated to the “bluer marshes” of Stage Harbor in Chatham.
If people can come together to help save horseshoe crabs for use in medical research, too bad drug companies don’t come together to save people instead of charging an arm and a leg for meds!