Spot a Horseshoe Crab

Most people think the only wildlife in New York are pigeons and pizza rats. But there are hundreds of species flying over, crawling under, and swimming around the city that never sleeps. Perhaps one of the most intriguing is the “living fossil” – the horseshoe crab.

The Atlantic horseshoe crab (Limulus Polyphemus) is actually not a crab at all. It is more closely related to spiders, ticks, and scorpions. It looks a bit like a flattened army helmet with a tail. Known as a “living fossil,” the horseshoe crab hasn’t changed much in the last 445 million years; they are thought to have evolved in the same ancient seas as the trilobites.

Getting Under the Hood

What has six pairs of claws, nine eyes, and a tail that can sense light? That’s right, our horseshoe crab. The crab uses its first pair of armlike claws for feeding, four pairs for walking, and the last pair for pushing. It has book gills (so named as they are shaped like the pages of a book) which store small amounts of water. These gills allow the horseshoe crab to breathe for a short amount of time on land.

Its long tail, the “telsen,” is not dangerous. The crab uses it to steer while in the water and to right itself if it gets flipped over on land. If you see a horseshoe crab upside down and struggling, you can flip it over to help it on its way. Be careful not to grab a horseshoe crab by its tail as you can injure it that way.

Full Moon Party at High Tide

Horseshoe crabs come ashore to mate on New York City beaches in May and June of each year.  Mark your calendars as this is a sight to behold.  Females leave the water with males grasping the backs of their shells. Sometimes a second, third, or even fourth male will hold on to the female and bodysurf up the beach in a crab conga line.

“When the amorous crabs hit the beach, they look like a sinewy, brown subway train pulling in for a station stop.”  – Margaret Mittlebach & Michael Crewdson, Wild New York

The best time to see the horseshoe crab mating is on a full or new moon at high tide. The females glide in on the high tide to travel far up the beach and dig a nest to lay tiny green eggs. Males crawl as quickly as they can to be the first to fertilize the eggs. Afterwards, the tide takes them back out into deeper waters.

In a couple of weeks, at the next highest tide, the crab eggs hatch and the tide sweeps the newborns out to sea. That is, if the eggs hatch. The eggs are an important food source for migrating shorebirds. Some biologists think that some shorebirds’ long-distance Arctic migrations are timed perfectly to feast upon the eggs of horseshoe crabs.

After the Party Is Over

Horseshoe crabs spend most of their lives wandering around on the bottom of the North Atlantic coastal shelf, eating mollusks and worms. Your best bet of seeing a live horseshoe crab is during mating season in May and June.

Don’t worry if you missed it this year. You have a great chance of seeing the remnants of horseshoe crab on any of our city beaches at any time. A horseshoe crab molts its shell 17 times before it reaches adulthood at about nine years old. The abandoned shells you see on the beach may not be corpses, but just a shell the crab had to shed before growing a new one.

Biologists estimate that a horseshoe crab can live up to 40 years. That’s a lot of Full Moon parties.

Places in NYC to See a Horseshoe Crab

You have a good chance of seeing a horseshoe crab shell on any city beach.

Here are the best places in NYC to see the horseshoe crabs mating in May and June:

  • Plumb Beach, Brooklyn
  • Twin Islands / Orchard Beach at Pelham Bay, Bronx
  • Calvert Vaux Park, Brooklyn
  • Jamaica Bay, Queens
  • Dead Horse Bay, Brooklyn
  • Great Kills, Staten Island

You can learn more about the monitoring of horseshoe crabs at New York Horseshoe Crab Monitoring Network.

Have you ever spotted a live horseshoe crab in NYC?  Saw a molted shell? I’d love to learn where you saw it or what you think in the comments below.

2 Comments

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  1. Highly fascinating! I’ve never heard of it. Nine eyes, Geez!, almost like it’s from a different planet. 🙂 Thanks for the information. I learned something new from blogging once again.

    Like

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