Why You Should Care About Horseshoe Crabs

single horseshoe crab in the ocean
Photo courtesy of the Delaware Center for the Inland Bays
Despite their appearance — with their armored shells and spiked tails — horseshoe crabs won't hurt you. 

If you vacation at the shore on the East Coast, you may have seen horseshoe crabs washed up on the beach — and you may have found them a little creepy. They're up to a foot wide; they've got that long, pointy tail; and underneath, there are all those legs!

Well, the strange-looking animals can't hurt you. In fact, they have actually helped you. They're critical to the pharmaceutical industry and play an important role in the ecosystem. And if you want to see a whole lot more of them, now's the time. You can even help researchers who keep track of the numbers of these creatures.

A Misnomer

Horseshoe crabs aren't actually crabs. "They're more closely related to spiders and scorpions," horseshoe crab expert Dr. William Hall says. There are four species in the world, one of which lives on the East Coast, from Maine to the Yucatán Peninsula, with the majority of the population in the middle of the range, in Delaware. The other species live in the Western Pacific.

If they look prehistoric, there's a reason: They've gone unchanged for a very long time. The species of horseshoe crab alive today have been around for 30 to 35 million years, according to Hall. And though they look a bit intimidating, they can't harm you. "The tail is not there to stick you; it's there to flip them over," Hall says. "They have claws underneath, but you can put a finger in a claw and they can't squeeze it hard enough to hurt you."

Important to Health and the Environment

Horseshoe crabs are essential to making a product that is used to test medical products for contamination. The product, called Limulus amebocyte lysate, or LAL, is made from the blood of horseshoe crabs, which are captured from the wild, then returned to the ocean after their blood is drawn. LAL is used in a test that detects bacterial endotoxins. "Any drug that crosses a cell membrane (like an injection of penicillin), a tooth implant, a hip implant, fluid that goes in your eye for your contact lens — [they all have] to be tested to be free of bacteria, and this is the most sensitive test we have," Hall says. "That product, depending on whom you talk to, is anywhere from a $100 million to a $150 million industry a year."

The crabs are also important to the ecosystem, largely because of their spawning behavior. In the spring, they come ashore in huge numbers to lay eggs. "When you get out there on a night when they're really coming ashore, you could see 10,000 or 15,000 crabs," Hall says.

The peaks occur with the new moon and the full moon, when the tide is at its highest, says Eric Buehl of the Delaware Center for the Inland Bays. "At high tide, the female moves in and kind of burrows in and starts laying eggs," he says. "The males have special claws that are able to attach to the females' shells, and they ride along. And as she's laying eggs, they're fertilizing them."

The eggs provide food for other animals at a crucial time. "There are a number of bird species that time their travels in their migration north to the spawning because it's a major food source," Buehl says. Hall explains that the eggs and young crabs are also important food for other marine creatures. "They're a huge source of protein for fish recovering after the winter, and once the eggs hatch, the juveniles are food for juvenile fish." He says it's not unusual to find the crabs inside sharks, rays and marine turtles.


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