These delicate, otherworldly creatures  are just starting their lives --   twitching and twirling inside  their translucent homes.

They’re baby horseshoe crabs, preparing  for the moment they can break free.

It all started two weeks ago, when  the tides were at their highest.

Horseshoe crabs emerge from the briny deep.

And head for the shore with  only one thing on their minds.

A springtime spawning spree.

These Atlantic horseshoe crabs gather, by the millions,   along the east coast of North America  -- from Maine to the Gulf of Mexico.

The crowds here in Delaware  are some of the biggest.

The males show up first, hanging out on  the beach and in the shallows of the bay.

They scramble to latch on to  the backs of passing females.

The females can be the size of dinner  plates, way bigger than the males.

Success!

They take advantage of the fleeting  high tides to haul their precious cargo   as high up the beach as possible.

The females muscle their way up  the beach, with the males in tow.

The greatest danger for these horseshoe crabs   is flipping over, exposing  their vulnerable underside.

And it only takes a small wave to do it.

Under the hood, horseshoe  crabs’ legs end in pincers.

But mature males have something  special on their front legs… This “clasper” that looks like a little  boxing glove with a hooked finger.

It’s perfect for gripping  the back of a female’s shell.

To flip back over, the animals use  their long, spiky tail, called a telson.

It looks a little scary, but  horseshoe crabs don’t sting.

Horseshoe crabs have been making these high tide   treks under the glow of the full  moon since before the dinosaurs.

That’s more than 400 million years ago.

Not everyone finds a date.

Especially those younger males.

But they hike up the beach anyway in  hopes of getting in on the action.

This female is dragging around two admirers.

When a female finds a good spot,  she digs and digs into the wet sand.

The female lays roughly four  thousand eggs in one go.

The male that clung to her all this time is in  the best position to fertilize the most eggs.

All those single dudes crowd around  too, vying to fertilize the rest.

As the party winds down, the  grownups start heading back to sea, But they’ll return for more of these  high tide soirees throughout the season.

They leave their fertilized eggs  behind, buried in the damp sand.

Each one is smaller than a pea Over the next couple of weeks  the embryos inside develop.

By the time the high tides return  -- these larvae are ready to hatch.

The jostling of the waves stimulates  them to break out of their shell.

This is their chance.

They have just a few hours to scramble into the  turbulent surf, before the high tide recedes.

They’ll mature beneath the  waves for roughly a decade   before they’re ready to  return as adults themselves.

… where they’ll take their turn in this  ancient dance of the moon, tides and sand.