Looking for a little offbeat action at the beach this weekend? It's not too late to catch the annual spring orgy of horseshoe crabs. If you haven't witnessed it before, it's quite a sight, I can tell you.

Like clockwork, these helmet-shaped creatures with the spiky tails haul themselves out of the the water from mid-May to mid-June to couple. You can see them day or night during that time, but mating peaks during the full and new moon cycles, with the highest numbers flocking to the shore during the evening high tides.

It's GP-rated sex, for those worried about what the kids will see. The females trundle to the edge of the lapping waves, often with one or more smaller males hanging on for dear life, and proceed to burrow into the sand to lay their eggs. Males surround the females and fertilize the eggs.

This is a great opportunity to see nature in action and observe how interconnected the web of life is. Horseshoe crabs (scientific name Limulus polyphemus) are some of the world's oldest creatures, tracing their lineage back 300 million years - long before dinosaurs roamed the earth.

Here along the mid-Atlantic coast, the crabs' mating frenzy helps sustain flocks of shorebirds, such as sandpipers and red knots, which stop off to rest and feast on the crabs' eggs as they fly from South America to northern Canada and the Arctic.

The crabs' comings and goings have become a topic of intense interest among biologists and conservationists, because many think their fate is linked to that of the shorebirds that depend on them for food at a crucial stage in their annual migration.  Red knots, in particular, have been in decline, which has led to restrictions on commercial harvest of the horseshoe crabs. The crabs aren't a table treat for people, but they've long been collected by fishermen to be used as bait to catch eels and other fish.

You can see the crabs coming to shore on quiet beaches along Chesapeake Bay at Sandy Point State Park or Eastern Neck Wildlife Refuge.  The best places to see the most crabs, though, are along the Delaware Bay shore, at places like Bowers, Fowler and Slaughter beaches.   My wife and I visited Slaughter Beach last weekend on a moonless evening and saw clumps of crabs all along the water's edge, like the one I photographed above.

To learn more about the crabs, and where to see them, go here.