Invertebrate

Atlantic Horseshoe Crab

Limulus polyphemus

Also known as American Horseshoe Crab, Horsefoot, King Crab

Atlantic horseshoe crabs are ancient marine arthropods closely related to spiders and scorpions rather than true crabs. Each spring, mass spawning events bring millions onto sandy Atlantic beaches during high tides around full and new moons, where females lay tens of thousands of eggs. Their copper-based blue blood plays a critical role in biomedical safety testing, making them an essential subject of coastal ecology and medical conservation.

MarineCoastalAncient Species

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VulnerableConservation status

Key facts

Diet & preyPolychaete Worms, Clams, Small Crustaceans

Predators

Red Knot
Gulls
Tiger Shark

ThreatsOverharvesting for eel and whelk bait, biomedical harvest stress, shoreline development, and sea level rise

HabitatsShallow coastal ocean waters, estuaries, brackish bays, and sandy intertidal beaches

Life span20–40 years

Classification

FamilyLimulidae
SpeciesLimulus polyphemus

Range & activity

Range data is not available yet.

Safe observation

Interaction riskLow

Low
Moderate
High
Very high

Why interaction risk is low: Safe to observe at a normal distance.
What to notice: Look for a broad brownish domed shell with a long tail spine in shallow water or along sandy shorelines.
Support conservation: Never pick up crabs by the tail as doing so causes joint injury, and leave spawning pairs undisturbed.

Responsible observation

Help Overturned Crabs: Gently flip stranded crabs upright by holding the sides of the shell, never the tail.
Observe Night Spawning: Visit sandy beaches during full or new moons in late spring to watch mass spawning.
Give Nesting Sites Space: Walk carefully along high-tide shorelines to avoid stepping on buried egg clusters.

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