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On a June afternoon, during high tide at Jamaica Bay in New York, a crowd gathers to watch the mating ritual of one of Earth’s most ancient creatures. Undeterred by onlookers, American horseshoe crabs scoot around like bumper cars in the surf until they collide with a mate. A male latches onto a larger female, holding tight in the roiling waves. She finds a suitable place to dig into the sand and, as she lays thousands of eggs, he fertilizes them.

These helmet-shaped arthropods—not really crabs, they’re more closely related to spiders—have survived 5 mass extinctions and for more than 400 million years. And yet, today, across much of their range they face the threat of being wiped out.

Habitat destruction has taken a toll, but so has overharvesting. Commercial fishermen argue that the crabs, which inhabit the Atlantic coast from Maine to Mexico, are the only viable bait for conch, whelk, and eel. Biomedical companies rely on a compound extracted from horseshoe crab blood, called LAL, to test for toxins in vaccines and other injectable drugs. In the Delaware Bay, home to the world’s largest spawning events, this combined pressure has caused crab numbers to plummet by two-thirds, according to the Center for Biological Diversity (CBD).

That’s especially bad news for Red Knots, threatened shorebirds that rely on horseshoe crab eggs to fuel migrations that can exceed 9,000 miles from South America to the Arctic. Immense flocks stop each year to feast along the East Coast, but those masses have dwindled as the density of available eggs has fallen sharply. When the birds can’t find enough food, they arrive at their breeding grounds in poor condition, if at all, says Erin McGrath, policy director at . “Then they can’t reproduce, and the numbers keep going down.”

Now conservationists are in the thick of a multi-pronged push to save both species. Central to that effort is replacing existing restrictions on horseshoe crab harvesting with more rigorous bans. In the past two years Connecticut, South Carolina, and Massachusetts have imposed partial bans, and an interstate regulator maintained a prohibition on harvesting female crabs in Delaware Bay. Despite major pushback from industry, the New York State Assembly in June passed a near-complete harvesting ban championed by ̽����ѡ and other conservation groups, the strongest protections of any state yet. still needs Gov. Kathy Hochul’s signature before it becomes law.

CBD and allies are also urging the federal government to as endangered or threatened, and to designate habitat critical to its survival. The group has also , and is planning lawsuits in other states, to seek transparency about how many crabs die when biomedical companies bleed them for the LAL compound—estimates range up to 30 percent—before releasing them back to the ocean. 

Such deaths could be avoided, environmentalists say, by fast-tracking FDA approval of synthetic alternatives to LAL that drug companies have already developed. An industry group that sets standards for safety testing took a big step in July by for using those synthetics—recommendations the FDA will likely adopt.

There’s much more work to do, experts say. Taken together, though, these actions could go a long way to ensure that a species far older than the dinosaurs isn’t lost within a single human lifetime.

This piece originally ran in the Fall 2024 issue as “Turning the Tide.” To receive our print magazine, become a member by .