Horseshoe Crabs


Despite its common name, the horseshoe crab (Limulus polyphemus), is more closely related to spiders and scorpions than crabs. All are invertebrates from the phylum Arthropoda, or arthropods. This group of animals includes insects (Insecta); spiders, scorpions, ticks and mites (Arachnida, or arachnids); crabs, lobsters, shrimp and barnacles (Crustacea, or crustaceans); and the 4 world-wide species of horseshoe crabs (Merostomata).

Horseshoe crabs are an ancient species. For over 300 million years (at least 100 million years before there were dinosaurs on earth) horseshoe crabs have roamed the world's oceans and and look today much as they have through the millennia.

Learn more about the natural history of horseshoe crabs.


Fun Horseshoe Crab Facts

Did you know that horseshoe crabs have blue blood? The protein (hemocyanin) that carries oxygen in horseshoe crab blood contains copper. When oxygen binds to the copper, the blood turns blue. As the oxygen is removed from the copper (as the blood circulates and delivers oxygen to the tissues of the horseshoe crab) the blood becomes colorless. The protein (hemoglobin) that carries oxygen in human blood contains iron. When oxygen is bound to the iron, human blood is red. As the oxygen is removed from the iron, the blood becomes blue.

The name horseshoe crab refers to the shape of the animal. The front half of a horseshoe crab looks like a horse's hoof or a horseshoe.


Learn More

  • Horseshoe Crab: History & Biology/Shorebird Connection/Human Use/Research/Fisheries Management
  • Horseshoe Crab New York State Fishery and Regulations
    New York State Department of Environmental Conservation
    (Fire Island National Seashore is one of the areas now closed to the harvest of horseshoe crabs in New York)

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