Horseshoe crabs are quite endearing-looking little critters that also have quite a peculiar appearance. But, dig deeper, and you’ll find that they are also fascinating animals.

  • Horseshoe crabs are older than time (or at least older than dinosaurs), having been around for over 300 million years.
  • Even though these crabs have a tough exoskeleton and look like crabs—they are not crustaceans. These critters have ten legs. This last feature means they are less crab and share more genetic material with spiders and scorpions. 
  • The horseshoe crab takes its name from the shape of its head, which looks a little like a horseshoe.
  • Its body has three parts, the head (prosoma). This head contains most of its biological organs, nervous system, heart, brain, and mouth.
  • This crab has nine eyes distributed throughout its body. The two prominent eyes are at the front of its head and are compound. The other seven eyes are not complex but are valuable in picking up movement to catch prey and detect changes in light.
  • It even has light receptors close to its long tail, which are excellent at sensing its environment.
  • The central section of its body is the abdomen (opisthosoma). The belly resembles a triangle containing a prominent ridge, with spines around its perimeter. The stomach includes gills to breathe and muscles to aid movement.
  • The last section is its long, pointy tail (telson). The primary purpose of the tail is to right itself in case it flips over.
  • Horseshoe crabs sustain themselves on a diet of algae, clams, and worms.
  • Female crabs are approximately one-third larger than males, reaching sizes of up to 19 inches.

If you’re ever in Delaware Bay with a full moon, new moon, at high tide during May or June, you may be lucky enough to see horseshoe crabs. They come out to breed at this time—perhaps because the full moon puts them in a romantic mood.