Horseshoe Crabs Remain Mysteries to Biologists

Misty Edgecomb
Bangor Daily News (Maine)
June 21, 2002

When the new moon rises in June, thousands of prehistoric creatures emerge from the depths of the sea, their heavy armor clanking as they clamor over one another in the shallows of Taunton Bay, Maine. There they mate, leaving hundreds of thousands of green eggs in the sand. Then, they simply disappear.

Remarkably, this is all modern science can tell about the horseshoe crab in Taunton Bay or anywhere else.

How long horseshoe crabs live, whether they return to the beach of their birth for spawning, why their life cycles seem directed by the moon, where they disappear to for the other 10 months of the year—all these questions remain mysteries.

Somehow, the horseshoe crab has thrived for 500 million years, and Sue Schaller wants to know why.

"You've got an animal that predates dinosaurs by 200 million years, and it hasn't changed much at all. It hasn't had to evolve," said Schaller, a biologist who has studied Maine's horseshoe crabs for the past three years.

One rainy afternoon recently, Schaller and four local volunteers, dressed in slickers and hip waders, are hiking along the shore of Taunton Bay near Shipyard Point in Franklin.

It's the height of the spawning season, and Schaller's crew is peering into the cloudy water, looking for the green-brown, helmetlike shells of visiting horseshoe crabs.

"They vacation on the bay," Schaller jokes.

The biologist finds a mating pair, a small male grasping a larger female in hopes of being nearby when she begins to release her eggs. As Schaller turns the crabs over, they gesture threateningly with long spike-like tails, known as telsons. They flap their hinged shells, and wave the pincher-tipped walking legs and daisylike swimmerets that surround their mouths.

The horseshoe crab is the sort of fanciful, frightening creature that appears more frequently in science fiction stories than in zoology texts.

"I love 'em," Schaller said. "Once you scratch the surface and get over the fear thing, they really are intriguing."

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