Horseshoe crabs may look scary, but when it's springtime in Delaware Bay, millions of these arthropods show they're lovers, not fighters. They lay masses of bluegreen eggs up on the shore. At just the right time, they pop and release the larvae within the sea.

WATCH our crab collab episode with OVERVIEW on‪@pbsterra‬!    • Why Are There 30 MILLION Horseshoe Cr...  

DEEP LOOK is an ultraHD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Explore big scientific mysteries by going incredibly small.


Each spring during May and June, Atlantic horseshoe crabs gather by the millions along the East Coast of North America with only one thing on their mind — a springtime spawning spree!

From Maine to the Gulf of Mexico they seek out calm bays and estuaries, waiting for the highest tides to emerge from the waves. They dig down into the wet sand and deposit huge numbers of peasized eggs.

David R. Smith, a biological statistician who studies horseshoe crabs for the U.S.Geological Survey, has come to Slaughter Beach, Delaware, to witness the spectacle under the glow of a full moon.

“It's sort of like looking back in time,” says Smith, “That same scene of these marine creatures coming to the water's edge on a quiet sandy beach to spawn has been repeated for millions and millions of years without much variation.”

What do horseshoe crabs eat?
Horseshoe crabs mostly eat worms and mollusks from the seafloor. But they aren’t picky, they’ll eat other things like small fish and different crustaceans.

Why do horseshoe crabs lay their eggs on land?
By laying their eggs in the damp sand, they protect their eggs from the many predators that live in the sea. It allows their offspring a chance to develop before another high tide carries them into the sea.

Why do horseshoe crabs have blue blood?
Like other mollusks, horseshoe crabs have blood that carries oxygen using a coppercontaining protein called hemocyanin. The hemocyanin turns blue when exposed to oxygen. Vertebrates like humans have ironcontaining hemoglobin in their blood, causing it to turn red when exposed to oxygen.

+ Find additional resources and a transcript on KQED Science:
https://www.kqed.org/science/1976488/...


+ More great Deep Look episodes:

These Fish Are All About Sex on the Beach | Deep Look
   • These Fish Are All About Sex on the B...  

For Pacific Mole Crabs It's Dig or Die | Deep Look
   • For Pacific Mole Crabs It's Dig or Di...  

Decorator Crabs Make High Fashion at Low Tide | Deep Look
   • Decorator Crabs Make High Fashion at ...  

+ Shoutout!

Congratulations to the following 5 fans on our Deep Look Community Tab for correctly answering that the body part a male horseshoe crabs use to grab onto their mates is a clasper, a modified pedipalp!

Sinister Omen
SARA FATIMA
Anirudh Anilkumar
Uwis Qurni Abdullah
hudson urruttia

+ Thank you to our Top Patreon Supporters ($10+ per month)!

Chris B Emrick
Burt Humburg
David Deshpande
Karen Reynolds
Daisuke Goto
Adam Kurtz
Allison & Maka Masuda
dane rosseter
Wild Turkey
Berian James
Nathan Jewsbury
Companion Cube
Tianxing Wang
Josh Kuroda
Mark Jobes
Cindy McGill
Blanca Vides
Kevin Judge
Jana Brenning
Supernovabetty
Titania Juang
Aurora
Anastasia Grinkevic
monoirre
Roberta K Wright
Leonhardt Wille
Syniurge
Rick Wong
KW
Carrie Mukaida
El Samuels
Mehdi
Kristy Freeman
Gerardo Alfaro
Nicky O.
Mary Truland
Cristen Rasmussen
Scott Faunce
Ed Gandia
SueEllen McCann
Jeremiah Sullivan
Noreen Herrington
Kelly Hong
Misia Clive
Shelley Pearson Cranshaw
Sonia Tanlimco
Kallie Moore
Teresa Lavell
Nicolette Ray
Laurel Przybylski
Louis O'Neill
Carlos Carrasco
Caitlin McDonough
Delphine Tseng
Elizabeth Ann Ditz
Joshua Murallon Robertson
Levi Cai
TierZoo
Silvan
chckncurry

+ Follow KQED Science and Deep Look:

Instagram:   / kqedscience  
Twitter:   / kqedscience  

+ About KQED

KQED, an NPR and PBS affiliate in San Francisco, California, serves Northern California and beyond with a publicsupported alternative to commercial TV, radio and web media.

Funding for Deep Look is provided in part by PBS Digital Studios. Deep Look is a project of KQED Science, the largest science and environment reporting unit in California. KQED Science is supported by The National Science Foundation, the Dirk and Charlene Kabcenell Foundation, the Vadasz Family Foundation, the Gordon and Betty Moore Foundation, Campaign 21 and the members of KQED.