S.C. Sea Grant Consortium

Stranded Horseshoe Crabs

What are Horseshoe Crabs, and Why do they Get Stranded?

Horseshoe crabs, whose scientific name is Limulus polyphemus, are prehistoric-looking shelled animals that have existed virtually unchanged in appearance for over 400 million years.

In the spring of the year, during very high tides, horseshoe crabs gather on the beach to spawn and may become stranded.

Flipped horseshoe crabs.

Horseshoe Crabs Can Become Stranded and Die

If the weather is rough a horseshoe crab may get flipped over (its legs facing the sky). With their energy drained from spawning, it can be difficult for them to right themselves, particularly if they are somehow impaired (i.e., broken tail).

During rough weather, up to 10% of crabs that approach the beach may become stranded. If stranded horseshoe crabs can be flipped back over before the heat of the day and make their way back to the water they may be able to survive.

How to Flip a Horseshoe Crab

When handled properly horseshoe crabs are harmless. Grasp both sides of the shell of the head portion of the animal, pick the animal up, and set it down with its legs facing the sand.

Don’t ever pick up a horseshoe crab by its tail! You risk damaging its tail and it won’t be able to flip itself over in the future.

Don’t get your fingers in the area between the head and the abdomen. This is where the crab bends and you could get your fingers pinched.

A person flips a horseshoe crab.
Horseshoe crabs on beach.

Just the Shell?

The off-cast molts of horseshoe crabs may be encountered on the beach. These are not dead crabs, but rather the shell that has been shed by a crab needing to grow. Horseshoe crabs molt several times during their first year and once a year afterwards.

Report Tagged Horseshoe Crabs

Always check horseshoe crabs for a tag, located near the back of the head section. Follow the directions on the tag for reporting the stranding. Tag studies help with managing the fishery.

Horseshoe Crabs Saving Lives

In South Carolina, horseshoe crabs are gathered for their blood, which is able to detect contamination in intravenous drugs and vaccines, making it vital to human health.

Much like when humans donate blood, horseshoe crabs are collected, bled, and then returned to the sea within a day. Horseshoe crabs are critical to the biomedical industry, and the humane bleeding process implemented achieves survival rates in excess of 80-90%.