Limulus polyphemus
Horseshoe Crab Survey 2011

Delaware Bay

Each spring hundreds of thousands of American Horseshoe Crabs migrate to the Delaware beaches to spawn as they have been doing for 300 million years. As a female comes in to the shore, a male grabs ahold of her and she pulls him along. Sometimes several males will be attached to one female and she pulls them all along. The female stops every few feet on the beach to dig a hole and deposit up to 20,000 shiny green eggs. The males then fertilize the eggs.

At the same time, thousands of migrating shorebirds arrive at the coast. They are on their way North after spending the winter in the Chile, Brazil, and Venezuela. After flying non-stop for several days, over 10,000 miles, they are very hungry and feast on the millions of tiny crab eggs, worms, and clams. After three weeks of eating they head North to the Artic to nest.
Crab Eggs

Learn More From the University of Delaware, Sea Grant, and NOAA

Crab Facts:
  • Crabs are not crabs at all - they are most closely related to a scorpion or tick or land spider.
  • They can go a without eating.
  • They are full grown adults between 9 and 12 years.
  • They have blue blood which is extracted (without harming the crab) and used for testing medicines.
  • Chemicals in their shell are used to speed blood clots (scabs) in humans and to make absorbable sutures (stitches that don't have to be taken out-they go away on their own).
Removing Blue Blood
Crab Track in the Sand

How do you know if the crab is a boy or a girl?
  • Males are smaller, females are larger (up to 2ft and 10lbs).
  • Boys have a curve under their shell, girls do not have a curve.
  • Males have front claws that look like a closed fist, females have front claws that look like scissors. (boys box, females sew)
Male Claws at the Top

Female on Left, Male on Right

Large Female in the Center with Surrounding Males

One Female Three Males