June 11, 2026 — 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.”
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.