Horseshoe Crabs

Horseshoe crabs come to shore to spawn by the light of the full moon

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.

Notice to Visitors: The harvest of horseshoe crabs is prohibited within Fire Island National Seashore.

What should I do if I see a horseshoe crab flipped over?

If you encounter a horseshoe crab flipped on its back simply flip it over. The best way to slip them over is by the edge of their shell. It’s important to remember that these creatures will not bite or sting you, and not to flip them by their tail. Their tail (or telson) is very delicate and can be easily harmed or damaged.

Have you seen horseshoe crabs on Fire Island?

If you have, you can help us! You can find these “living fossils” spawning on Fire Island in early May and June. If you see a horseshoe crab keep your eye out for a circular tag on their shell. If you see a tag snap a picture! You can report the information you collect here:

Researchers have been tagging horseshoe crabs to learn more about their survival, movement and management. By partaking in citizen science and reporting these horseshoe crabs you are contributing important information to scientists.

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3 minutes, 16 seconds

Take a closer look at horseshoe crabs and the citizen scientists helping us learn more about the spawning population on Fire Island in this short 3-minute video.


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.


Last updated: November 21, 2020

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