Ingo Arndt / Rear view of Horseshoe crab (Limulus polyphemus) with trail in sand, Delaware Bay, Delaware, USA, May

Steve Nicholls / Horseshoe crabs (Limulus polyphemus) spawning at low tide, Slaughter Beach, Delaware, USA, May

Juergen Freund / Horsehoe crab (Tachypleus gigas) swimming on its back with gills creating the propulsion, Palawan, Philippines. Did you know? Horseshoe crabs are more closely related to spiders than crabs.

Juergen Freund / Horsehoe crab (Tachypleus gigas) underside, Palawan, Philippines

Magnus Lundgren / Wild Wonders of China / Staff from Ocean Park Conservation Fund, OPCF, and students visit Ha Pak Nai to see the juvenile Chinese horseshoe crabs, (Tachypleus tridentatus) Yuen Long District, New territories, Hong Kong, China...

Magnus Lundgren / Wild Wonders of China / Staff from Ocean Park Conservation Fund, OPCF, and students visit Ha Pak Nai to see the juvenile chinese horseshoe crabs (Tachypleus tridentatus) in a mudflats, Yuen Long District, Hong Kong, China.

Magnus Lundgren / Wild Wonders of China / Transpond reader (receiver) used to find the juvenile Chinese horseshoe crabs (Tachypleus tridentatus) before the release. Ha Pak Nai, Yuen Long District, Hong Kong, China.

Magnus Lundgren / Wild Wonders of China / Secondary school student interviewed by TV channel about the release of juvenile Chinese horseshoe crabs (Tachypleus tridentatus) that have been artificially-bred by City University of Hong Kong, and...

Magnus Lundgren / Wild Wonders of China / Secondary school students releasing juvenile Chinese horseshoe crabs (Tachypleus tridentatus) that has been bred by City University of Hong Kong, Ha Pak Nai wetlands, Yuen Long District, Hong Kong, Ch...

Alex Mustard / Toddler watching a pair of Horseshoe crabs (Limulus polyphemus) spawning in shallow water. Larger female and smaller male. Indian River, North Atlantic Ocean. Titusville, Merrit Island, Florida, USA....

Doug Wechsler / Horseshoe crabs (Limulus polyphemus) on beach mating, with Ruddy turnstone (Arenaria interpres) and Red knot (Calidris canuta) on beach, Delaware Bay, New Jersey, May.

Doug Wechsler / Dunlin (Calidris alpina) and Short billed dowitcher (Limnodromus griseus) feeding on Horseshoe crabs (Limulus polyphemus) eggs, Delaware Bay, New Jersey.