Horseshoe Crab

Limulus polyphemus

The Basics:

• Size: up to 20” long and 10” wide; females are larger than males.
• Color: Brown carapace (outer shell).
• Habitat: Salt waters and beaches.
• Where and when to observe:  May and June around area beaches like Jamaica Bay, Marine Park and Plumb Beach.

The Details:

They may look a little scary but there’s no reason to fear this fascinating creature that dates back 310 million years and is considered a living fossil.

Named for the shape of its brown carapace (protective outer shell), the Horseshoe Crab is actually related to spiders!  The carapace measures up to 20” long and 10” wide; females are larger than males.  They have 10 eyes but the most noticeable are on the carapace’s sides. Six pairs of jointed legs help them move along and the long, pointed tail isn’t for defense but instead used as a helpful lever if the crab is overturned.

Horseshoe Crabs are found along the bottom of the coastal shelf to the tide line, up to 75 feet deep, where they scavenge for mollusks, marine worms, algae, and dead fish.

Come May and June during the highest tides provided by full and new moons, females crawl onto beaches with males not far behind.  Females lay up to 300 olive green eggs, which are fertilized by males before the tide takes the adults back to the water.

Two weeks later, coinciding with the next high tide, hatchling crabs emerge and are swept into the ocean with the tide.

Horseshoe Crab eggs are a vital food source for migrating shorebirds.  However, their populations appear to be declining thanks to such issues as overharvesting for fishing and habitat loss.

But you can help Horseshoe Crabs!  First, don’t be frightened by their imposing appearance, but rather observe and learn about these fascinating living fossils.  Great places to visit them include Marine Park, Plumb Beach and Jamaica Bay.  If you see one overturned, give it a helping hand by turning it right side up.  Many organizations like the American Littoral Society offer Horseshoe Crab walks in May and June.

References:

• Field Guide to the Natural World of New York City by Leslie Day, published 2007 by Johns Hopkins University Press.
• The Horseshoe Crab by the Ecological Research and Development Group, accessed April 1, 2009 at http://horseshoecrab.org/.
• Wild New York: A Guide to the Wildlife, Wild Places and Natural Phenomena of New York City by Margaret Mittelbach and Michael Crewdson, 1997, Three Rivers Press.

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