Horseshoe Crabs Return to Cape May County

 

In this annual rite of spring, the beaches of Cape May and the broader Delaware Bay region play host to one of the oldest, most spectacular wildlife phenomena on Earth: the mass spawning of Atlantic horseshoe crabs (Limulus polyphemus).

This ritual has been repeated for nearly 450 million years—meaning these "living fossils" arrived on these exact shores long before the first dinosaurs walked the earth.

While horseshoe crabs begin trickling onto the beaches in late April, the main event happens in May and June. The absolute peak centers around the Full and New Moons, specifically during evening high tides. May 2026 has two Full Moons to start and end the month.

Driven by the high spring tides, tens of thousands of crabs emerge from the deep bay waters simultaneously. Large, smooth-shelled females crawl up to the high-tide line, often trailing one or more smaller males holding onto her carapace (shell) with specialized, boxing-glove-like claws. The female digs a shallow nest in the sand to deposit up to 20,000 tiny, greenish-tan eggs. The males then fertilize them as the waves wash over the cluster.

At its height, the shoreline looks less like a beach and more like a cobblestone street paved in dark, gleaming, olive-green helmets jostling in the surf.

The arrival of the crabs triggers a second, equally spectacular natural event. The Delaware Bay is the largest horseshoe crab spawning site in the world, and the millions of eggs left in the sand are a vital fuel source for migrating shorebirds.

Among these birds is the Rufa Red Knot, a threatened species undertaking an incredible 9,000-mile journey from the tip of South America up to the Canadian Arctic. Cape May is their ultimate refueling station. The birds arrive emaciated, having lost up to half their body weight. They gorge themselves almost exclusively on the lipid-rich, easily digestible horseshoe crab eggs that are churned up to the surface by the waves.

In just about two weeks, a Red Knot must double its body mass to survive the final leg of its journey north to breed. Without a dense concentration of crab eggs, the birds cannot successfully reach the Arctic or reproduce.

If you head down to the Cape May area to see it, the Delaware Bay side beaches (like Reeds Beach, Cook's Beach, or Higbee Beach) offer far more intense spawning activity than the oceanfront Atlantic beaches, as the crabs prefer the calmer, wave-protected waters of the bay.

Because both the horseshoe crabs and the shorebirds are highly vulnerable, many of Cape May's key bay beaches are seasonally closed to the public during the peak weeks to prevent disturbing the birds. However, public viewing platforms and guided walks hosted by organizations like the Cape May Bird Observatory offer spectacular front-row seats to this ancient dance.