Horseshoe crabs are one of the most familiar, if not beloved, animals in the Chesapeake. Their muddy, dun-colored shells plow through the eelgrass like barnacle-studded hubcaps, bristling below with a phalanx of terrifyingly jointed legs that wave feebly when the crab is turned over. From the top, they appear to be camouflaged, self-propelled shields, from the bottom they remind us how closely they're related to spiders and scorpions. The first settlers referred to horseshoe crabs as “Kings Crabbes” and some of the earliest images we have from European exploration of the Chesapeake show them awkwardly scuttling along the water’s edge, much as we see them today:
A detail from John White’s The Manner of their Fishing, painted in 1585 in region of modern-day Roanoke Island.
Traditionally, humans have found a few uses for horseshoe crabs, even though we haven’t managed to make a fritter, cake, salad or soup from their compartmentalized carapaces. From the 1800’s onward, Chesapeake and Delaware residents would descend to the water’s edge in the spring when the horseshoe crabs beached themselves to spawn and lay their eggs. Easily plucked from the sand and rendered totally ineffective once turned over, the crabs would be gathered by the thousands and processed for fertilizer or animal feed. In the 20th century, fisherman also found that the eggs of female crabs are a veritable caviar for eels and conchs. There was a subsequent run on horseshoe crabs female crabs, with the predictable results that their populations declined rapidly. Today, horseshoe crabs are protected in several states from harvest, and their numbers are steady.
Image of horseshoe crabs harvested for bait use, courtesy of Virginia Tech.
Far away from the brackish shallows of the Chesapeake, scientists have found uses for horseshoe crabs that would have been inconceivable to the watermen and farmers that processed them into field nutrients or chicken feed. In hospitals, doctors have used the crabs in eye research, the manufacture of surgical sutures, and the development of wound dressings for burn victims. Immunology labs have even become literal vampires of horseshoe crab blood, draining the crabs of their unique hemoglobin-free, blue-tinted plasma for use in the detection of bacterial endotoxins, which can cause severe immune diseases in human beings.
Horseshoe crabs being “milked” for their unique blood. The crabs are returned to the water after this process, with an 85% survival rate. Photo courtesy of fresh photons .
The most important use for horseshoe crabs, though, is as a critical part of the Chesapeake’s estuarine food chain. While they have no known predators when they mature, horseshoe crabs eggs sustain shore birds throughout the spawning season. Oystercatchers, terns, and sandpipers can be seen fixedly probing the sand with their beaks in the spring, seeking out the tender turquoise clusters of buried eggs. Conservation efforts are underway to on the shorelines of Delaware, Maryland, and Virginia to protect the horseshoe crab spawn by opening up expanses of beach that are currently rip-rapped, providing more places that the crabs can spread their bird buffet.
This video from Host our Coast explains more about the efforts to protect the Chesapeake’s “living fossil”, the horseshoe crab. And while they may never be described as beautiful (their latin name translates to “An askew giant with one eye”), the humble horseshoe crab’s value has never been in dispute.