What I never knew about horse shoe crabs


I knew they are one of the oldest living creatures, (them and cockroaches) that have survived in the same form for thousands of years.  I knew there is nothing edible about them, and that no part of them will hurt you unless they whip your shin bone with that hard, thick tail. I knew I had always seen them in brackish water around Ocean City when we went to areas like that to catch Maryland blue crabs.  I knew that lots of times we saw some that were mating, and lots of other times they were just there, not….connected.

Last week my son and daughter in law and I spent a week in West Ocean City, MD.  We rented a wonderful house that has a pier out into Sinepuxent Bay. (Old  Indian name, as many things and places in that area are.  Including another bay two bays up the coast, called Assawoman Bay. Seriously.)


So, one day when I was out back with the traps trying to catch Maryland blue crabs, I caught a horse shoe crab instead.

horse shoe crab

We looked him over and enjoyed seeing him for a few minutes and put him back in the bay.  That night we saw 2 pairs out back, just about dusk, mating.  We hadn’t seen any of them before that day, and wondered why now and why not before?  That, of course, led to an internet search!

horse shoe crab mating

The search told us about another time when mother nature is in charge, and knows things people will never understand.   Horse shoe crabs mate annually, between the full moons in May and June.  It was 2 nights before the full moon. We learned that once mated, she would lay 4 or 5 balls of eggs along the edge of the water, just close enough to get wet again with each high tide, and the high tides are 12 hours apart.  The sand she lays them in never has a chance to get dried out, but stays moist even at low tide.  She digs herself down into the sand to lay the eggs, and the small wave action along a bay (much smaller waves than at the ocean itself) isn’t strong enough to wash the sand away and uncover the eggs.

Each golf ball sized ball of eggs contain about 5000 eggs.  So in one night, she could lay 20K eggs.  They hatch in 2 weeks and are about the size of a lady bug when they hatch. Birds and other creatures will dig some up and eat them, so she makes sure there are plenty to keep her species going on. All up and down the east coast, on those nights, eggs are being laid.  Then the adults go back out to deeper water, which is where they spend their lives, unless it’s mating time.

We also learned they’re not crabs at all.  They’re more closely related to spiders than they are crustaceans.

If you’re at the beach, somewhere near some shallow water, and see a whole bunch of these, some of them …..connected, now you’ll know all about this amazing process.

8 responses to “What I never knew about horse shoe crabs

  1. Thank you! We’ve been going to the beaches my whole life and this was new to me. I’ll share one you may not know about crustaceans. A few years back we were on Lewes’s Delaware Bay and were stunned to see hundreds of empty crab shells early one morning. We asked a local crabber who said they climb out to sand, molt that old too-small shell, and go back to sea. I think it was September. I’ve since talked to seashore lovers, even some with homes there, and realized we saw an event many never get to see.

    • Thank you for your comment! I won’t eat the soft shell crabs cos all the innards are still in there, lol! That would be good to see when a bunch of them have shed their shells. And no, probably a lot of people don’t get to see a lot of them, so you really had a treat.

  2. Pingback: Lots of interesting animals along the shore of the bay | Sarasin's thoughts.......·

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