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Crash: A Tale of Two Species
A new PBS special explores the amazingly synchronized lives of two very different species. It airs Sunday, February 10, 2008, at 8 p.m.

Horseshoe Crabs mating.
© EBC 2008

Shiny and smooth, a hard brown shell shelters the vital organs and spiderlike legs of a primitive life-form slowly crawling from the water. A long, pointed spine trails behind, making tracks in the sand. Blue blood running through their veins, hundreds of these ten-eyed, leggy creatures venture toward the water’s edge to cover the beach in a monstrous mating ritual. As the ceremony eventually comes to a close and the creatures crawl back to the watery depths, airborne travelers, exhausted and hungry from a 4,000-mile flight, swoop down to partake in a delicious feast of eggs left behind.

This is not a scene from a sci-fi horror flick set on a far-off planet. Rather, it’s just one of the many captivating images depicting the relationship between horseshoe crabs and red knots—migratory shorebirds—in Allison Argo’s new film, Crash: A Tale of Two Species, which airs February 10, 2008, at 8 p.m. on PBS’s Nature series.

Horseshoe crabs on a beach.
© EBC 2008

The horseshoe crab is not really a crab. More closely related to spiders and scorpions, it’s actually an ancient arthropod, having survived for nearly 350 million years trolling the ocean floor since before dinosaurs walked the earth and flowering plants dotted the landscape. Today some fisherman use horseshoe crabs for bait, and scientists use its blood for biomedical research. Although its benefits to humans are many, the horseshoe crab also holds the key to the small red knot’s survival.

The red knot, a robin-sized sandpiper, migrates each spring from South America to the Arctic to breed. During the past decade red knot numbers have declined by 70 percent. Researchers were unsure what caused the population crash until they examined the relationship between horseshoe crab spawning and red knot migration.

Red knots on a beach.
© Mark Peck

Each spring, taking their cue from the moon-driven tides, horseshoe crabs drag themselves ashore to spawn. The females bury themselves in the sand to lay their eggs, and upon emerging, sometimes stir other egg clusters above ground. Just as the crabs return to their ocean home, red knots arrive to take a pit stop from their long migration. The tiny egg sacs left behind pack a protein punch, fueling red knots for the last leg of their arduous journey. Indeed, horseshoe spawning is perfectly timed with red knot migration, and over-harvesting of the crabs may have put the bird on a crash course to extinction.

Horseshoe crab eggs.
© EBC 2008

Now that this important relationship has been identified, a number of conservation efforts are in place. A moratorium on crab harvesting in Delaware Bay is in place, researchers are working to develop artificial horseshoe crab bait, (an alternative bait or a substitute bait?)and beach access is limited during spawning and migration season. The future of both species is still precarious, but researchers and conservationists hope their efforts will help bolster their populations before it’s too late.—Shawn Query

Click here for a podcast with filmmaker Allison Argo.

For more on the PBS special, including an interactive red knot migration map and videos, click here.

For more Audubon coverage on horseshoe crabs and red knots, read:

The Removable Feast,” by Jon Luoma

A Knotty Problem,” by Daniel Butcher

Life, a Journey Through Time,” by Frans Lanting

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