Limulus polyphemus.
Limulus polyphemus.

Horseshoe Crab


Horseshoe crabs are not really crabs, they more closely related to spiders. The horseshoe crabs and the arachnids together form the subphylum Chelicerata.

There are several species of horseshoe crabs, but they sort of look alike to me. The ones in the pictures above were labeled as Limulus polyphemus, the Atlantic horseshoe crab.

Horseshoe crabs have been around for a long time. Horseshoe crabs have been old when the dinosaurs first roamed the Earth and they still sort or look the same today.

Limulus polyphemus.

Atlantic horseshoe crabs (Limulus polyphemus), Ripley’s Aquarium of Canada.

As an animal that has been around so long, the horseshoe crab has various tricks up its sleeves. The amobocytes from the blood of the horseshoe crab can coagulate around bacterial endotoxins encasing such toxins and rendering them harmless. This has long been used to detect the presence of minuscule amounts of bacterial endotoxins and check for their absence on surgical equipment. This is called the limulus amebocyte lysate (LAL) test. To get the required limulus blood horseshoe crabs are captured in the wild and some of their blood is ‘donated’ after which the animal is released to the ocean again. So far an artificial substitute for horseshoe crab blood has not been developed although scientists are working on it because the blue blood ‘donated’ by wild horseshoe crabs goes for tens of thousands of dollars a liter.

Humans also study all sort of other aspects of the horseshoe crab anatomy and physiology for all the fascinating features these animals have. After all their design has proven to be successful for hundreds of millions of years.

Previously horseshoe crabs have been considered pests and people tried to kill them, which drove their number down to the level that now horseshoe crabs need protection.

Let it be a warning to us all. An animal that was previously considered to be a useless pest, and decimated by short sighted humans for no other reason than to drive their numbers down, now provides something that we need and cannot get from anywhere else. Doesn’t our earlier effort to kill them all look stupid in retrospect?

You can sometimes buy a horseshoe crab as a sort of novelty pet in stores that sell livestock for marine reef tanks but you probably should not get one. Horseshoe crabs can grow really large, around 20 inches, and bulldoze everything in their path as they walk around in a tank, so they are not really well suited for a home aquarium.

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Last updated: February 3, 2015

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