Big Brown...

is the nick name for the horseshoe crab. They have come to the beach to lay their eggs.
The Atlantic horseshoe crab (Limulus polyphemus), also known as the American horseshoe crab, is a species of marine and brackish chelicerate arthropod. Despite their name, horseshoe crabs are more closely related to spiders, ticks, and scorpions than to crabs.