Cape plays big role in research
Their scientific name, Limulus Polyphemus, is akin to saying “skewed glancing giant.” In English, horseshoe crabs are named for their likeness to the rusty shoes of horses.
They have survived for millions of years, through crashing continents, up-thrusting mountains, and diminishing seas. The common ancestor may have lived 450 million years ago.
Their cryptic cover contains an assortment of ten mysterious eyes to guide the male to its mates, to see prey, to sense ultraviolet light, to transmit information about light and dark to the brain of the animals. The front pair make them more akin to spiders and ticks than to true crabs which have stalked eyes.
They have five pairs of legs. The last pair are “walking legs.” The first pair are “boxing gloves” in the mature males and “scissors” in the females. (Males mature at eight years, and females at about ten. The females, larger than the males, in our area can grow to about a foot wide.) Two pair of smaller “brush ups” one at the posterior, one at the front, help push extra food into the mouth in the center of the body underneath.
Horseshoes do molt just like true crabs – many times when they are young, not at all when they are mature. You can see the eggshell fragile molts in the wrack line.
The animals grind up the food they eat with their upper legs. They often eat while swimming on their backs. They will eat just about anything dead or alive, including clams and clam worms.
The Cape has been in the forefront of Limulus research; scientists at the Marine Biological Laboratory in Woods Hole were awarded a Nobel Prize in 1967. In the 1960s research began on medical uses of their blood and the first company to use the findings was formed, Associates of Cape Cod, 35 years ago. The late Bob Barlow at MBL did breakthrough research on their eyes.
The Horseshoe Crab Conservation Association of Cape Cod has led in creating coalitions with organizations up and down the east coast, working especially with Massachusetts state agencies to create more stringent regulations for the crabs, and to educate folks about their conservation. Keep an eye out for their lectures. Mass Audubon also gives horse and pony shows about horseshoe crabs to children, which include a wonderful detachable toy.