Every year in late spring, America's Atlantic coastline hosts one of the animal kingdom's wildest orgies.

The sandy shores are taken over by thousands of horseshoe crabs who mate and lay clusters of eggs.

This feverish lovemaking might be part of why the species is so resilient.

Horseshoe crabs have been around for around 450 million years.

They were here before the dinosaurs

and survived a mass extinction

that wiped out 90% of life on Earth.

But lately, a new species has joined the party.

Humans.

Humans who are quite literally out for the horseshoe crab's blood.

They have this somewhat magical blood. It's used to do a lot of our pharmaceutical testing,

everything from COVID vaccines to insulin to any injectable medications that we use on our day-to-day basis.

Horseshoe crab blood has been called the medical equivalent of gold.

By one estimate, it's worth around $60,000 a gallon.

And the growing market for it is at the center of an ethical debate between environmentalists and

biomedical firms.

For the Freakonomics Radio Network, this is the economics of everyday things.

I'm Zachary Crockett.

Today, Horseshoe Crab Blood.

To better understand how Horseshoe Crab Blood became such a valuable commodity, I turned to an expert.

I'm Dina Fine Marin. I'm the senior reporter that covers wildlife crime at National Geographic.

Marin has spent her career looking into all kinds of offenses, rhino horn trafficking, dinosaur fossil heists, even leech smuggling.

...