Horseshoe Crab (Limulus polyphemus)

First of all, Horseshoe crabs are not really crabs. They are related to scorpions and spiders. Horseshoe crabs get their name from the resemblance of the shape of their shell to a horseshoe. Although Horseshoe crabs look frightening, they are actually gentle, harmless creatures. On the underside of their hard outer shell, there are a dozen pairs of legs, most of them with claws. The legs surround a centrally located mouth (also on the underside). Horseshoe crabs feed by burrowing in the sand with their legs to look for worms and shellfish. Their rear legs crush the shells of their prey, and their front legs place the food in their mouth. Horseshoe crabs have two pairs of eyes on top of their shell. Their eyes help them locate mates. They are not used much for locating food (this is done primarily by feel by their legs underneath their shell).

Horseshoe crabs have an interesting mating ritual. In late spring, males and females gather in large groups at the shore. Males grasp onto the back ends of the females' shells. The female walks up onto the beach with the male hanging onto her back. Every couple of feet, she stops and lays eggs in the sand. When she finishes laying and starts to walk forward again, the male, still hanging onto the female, releases sperm over the eggs, thus fertilizing the eggs. Horseshoe crab eggs are a very important source of food for migrating birds.

Although Horseshoe crabs have few predators in the wild, some populations of Horseshoe crabs are declining. People collect Horseshoe crabs for many reasons. Their shell is made of a substance called chitin. Chitin is sometimes used to make contact lenses, skin creams, hair sprays, surgical thread, and diet pills. Horseshoe crabs are also collected for blood removal and then returned to the water. Horseshoe crab blood contains a certain compound that kills bacteria and can be used to purify medicine.