The American Horseshoe Crab (limulus polyphemus) is one of 4 surviving species of the horseshoe crab worldwide and the only one in the Americas. It is not actually a crab, but a marine arthropod distantly related to spiders, scorpions, and sea spiders. Limulus polyphemus has been surviving and adapting on earth for around 445 million years—long before the dinosaurs.

The horseshoe crab has a segmented shell with a long spike tail that protrudes from the back of the carapace, or “shell". Many beachgoers initially fear the horseshoe crab because they think the tail is a stinger, but it is more like a rudder or an appendage that can help flip the creature back over, should it find itself upside down. They should NEVER be picked up by the tail because the joint attaching it to the shell can become dislocated. This will render the horseshoe crab defenseless. Underneath their shells, they have 5 pairs of legs and a pair of chelicerae, which are like arms that help move food into their mouths. They breathe using gills when they are underwater. Two pairs of eyes can be seen on the upper shell (carapace), and one pair of eyes are located on the ridges toward the sides.

However, the most interesting feature of the horseshoe crab is arguably their blood, which turns blue when exposed to oxygen. It is not the color that makes it special, buts its ability to make bacterial endotoxins helpless when they attack the crab. A chemical called limulus amoebocyte lysate (LAL) detects toxins and then coagulates the blood around the toxin so that it cannot harm the creature. LAL fights off bacterial endotoxins that cause fever, inflammation, venereal disease, bacterial meningitis, cholera, the bubonic plague, and countless other deadly diseases. No other animal’s blood is known to have such ambitious antimicrobial properties. Scientists in the 1970’s discovered that the LAL in the horseshoe crab’s blood could be used to make sure that ANY medical device, implant, vaccine, or medicine was safe to be put into a human body. So here is the problem for these creatures: Today every single drug or vaccine, or clinical trial or ANY finished solution that will be inserted into the human body MUST have LAL testing.

How do medical companies obtain this ‘blue gold?’

About 500,000-600,000 horseshoe crabs are collected annually from beaches and they are ‘bled.’ Up to about 30% of their blood is removed from their bodies and they are returned to the ocean. A significant number of these ‘bled’ creatures do not survive this process once returned to the water.

Medical companies have recently created a manmade version of LAL called rFC. The rFC can be used in place of LAL, but there are strict guidelines when using it with extra work needed to “pass the test.’ Scientists are hopeful that the use of rFC will become better studied and accepted so the world does not need to rely on bleeding the horseshoe crabs. Currently, the American Horseshoe Crab is considered ‘vulnerable’ to extinction. Research seems to point to a 30% population decline in just the last 4 years. The use of rFC would greatly improve the chances of the species’ ability to rebound in numbers.

The horseshoe crab must be protected in order to preserve human health and wellness. Beyond human health, shorebirds need the eggs of the horseshoe crabs for food during long migrations. Sea creatures make their homes on the shells of the horseshoe crabs. Coastal communities that rely on fishing for their economic health may use horseshoe crabs for bait for eel and conch fishing. The conservation of these iconic creatures is important to life on earth.

Interesting facts:

Their shells appear fluorescent under UV light.

Horseshoe Crabs grow by molting out of their exoskeleton (shell.)

Females are larger than males.

Newly hatched and young horseshoe crabs grow in the sand for a few years, before moving to the ocean.

Adult shells range from 3.5 inches to 33.5 inches in length.

The coarse sand on Massachusetts, NJ, and Delaware beaches is where many of the creatures spawn each year.

Horseshoe crabs can live 25 years.

Citations:

Washington Post 8/1/2021 Caren Chesler

Washington Post 2017 Sarah Kaplar

Hadley, Debbie. “The Horseshoe Crab, an Ancient Arthropod That Saves Lives.”

Thought Co, Feb. 16, 2021, thoughtco.com/horseshoe-crab-4147315