to injurious stimuli are interpreted as something other than affect—a reflex—and as such, compassionate care does not need to be rendered. Despite mounting evidence,5 this popular and intransigent belief among many humans that animals without backbones do not feel pain influences our dismissive treatment of 95% of the total number of species on earth.6 But returning to horseshoe crabs specifically, what are the other distinguishing characteristics of this species?
Horseshoe Crab Biology and Anatomy
The ocean-dwelling horseshoe crab of North America, Limulus polyphemus, is a strange-looking animal. It crawls along the ocean floor with its maroon helmet-like hard-shelled top, the carapace, made of chitin and proteins. It has 10 “eyes” and six pairs of legs and claws underneath. In addition to its two compound lateral eyes, its other eyes are light-sensing organs located on different parts of its body—the top of the shell, the tail, and near the mouth. These eyes assist the crab in adjusting to visible and ultraviolet light and enhance adaptation to darkness in various environments, aquatic and terrestrial.7 A crab uses a nonpoisonous 4–5 inch hard tail, called a telson, to steer or right itself when it is overturned.8 The telson is dragged in the sand as the horseshoe crab lumbers along the shoreline. Adult crabs weigh 3–5 pounds and are 18–19 inches in length from head to tail for females (males are a few inches shorter). They can live for about 20 years. During spawning, they are either on the beach around high tide or swimming in 2–3 feet of water. When not spawning, they crawl along the bottom of the ocean at depths of 20–400 feet.9 On the shore, they are “slow and easy to catch” making them an ideal species for field biologists to study and to engage students.
Despite their spiny and spiky exterior, they are also comical to human eyes. As described by the biologist Rebecca Anderson, the first time she worked with horseshoe crabs she “pretty much fell in love with them because they look like these fearsome creatures with armored bodies and all their legs, but they are ineffectual as defenders. And they look so adorable when they walk on land.” It is difficult for most humans to observe horseshoe crabs in the water, but they have been described as “rather graceful compared to their tank-like appearance when they come to the shore.”10 Omnivorous creatures, they eat mostly clams and worms. They do so by crushing and grinding their food with their legs—or, more accurately, their knees—and shoveling the food into their stomach.
Anatomical illustration of the horseshoe crab. Illustration by C. Ray Borck.
Globally, there are four species of horseshoe crabs living on the continental shelf—one in North America, Limulus polyphemus, and three in Southeast and East Asia. The three species of horseshoe crab in Asia are Tachypleus gigas, Tachypleus tridentatus, and Carcinoscorpius rotundicauda.
Some humans have been drawn to the horseshoe crab because it unlocks secrets about the “sea of life.” With a fossil record to verify its ancient lineage, the horseshoe crab is among the oldest old. According to geologist Blazej Blazejowski, when traced by looking at modification by descent, crabs haven’t changed morphologically over tens of millions of years and as such are stabilomorphs, organisms that are morphologically stable through time and space. Their closest relatives are trilobites, which lived from 510 millions years ago. Amazingly, the horseshoe crab has survived longer than 99% of all animals that have ever lived.11 One of the reasons the species have survived for so long is because of the composition of horseshoe crab blood cells called amoebocytes. The blood is copper based, and when it hits the air it turns blue. Because of the chemicals in the ameoboyctes, the horseshoe crab’s blue blood coagulates when it detects contamination. This instantaneous reaction to threat through clotting protects the animal from harm. It is this very quality of their blood, the ability to transform into a biopharmaceutical gel, that has been used to insure the safety of all injectables and insertables in human and veterinary applications.12
These ancient species are also remarkable because they are primarily aquatic, coming onto the shore for spawning and nesting for brief periods every year. Indeed, if we accept the anthropologist Stefan Helmreich’s definition—“the alien inhabits perceptions of the sea as a domain inaccessible to direct, unmediated human encounter”—then horseshoe crabs are aliens.13 Unlike many domesticated animals or pets, these aliens are not intimately knowable since their primary place of residence is uninhabitable by humans. Adding to their alien-ness, horseshoe crabs are not easy for the layperson to categorize. They live in the sea, but some suggest they look like spiders. They are sometimes attached—“amplexed”—to one another. (You find yourself asking, Is one of them a baby? Is it catching a ride? Are they fighting? Are they mating?) They are prehistoric, and yet they seem so vulnerable. On land, they are practically defenseless, writhing helplessly when upside down with their fragile bits exposed to hungry birds.
Contrary to their name, horseshoe crabs are not true crabs. They are not even crustaceans. Taxonomically they belong to the same broad category that crustaceans do, the phylum Arthropoda—meaning that as invertebrates they have no backbone or inner skeleton; they have jointed legs and a hard outer shell, an exoskeleton, which protects a soft body. Horseshoe crabs are chelicerates, belonging to the same group that includes ticks, spiders, and scorpions.
After spawning during high tides in March through July, the North American species buries its eggs, which develop within the beach sediments after a couple of weeks to reach the trilobite (first instar) larval stage.14 They become reproductive adults after 16–17 molts or 8–10 years—which is slow growing for a marine invertebrate. Molting is the process of shedding the old shell and emerging from it with a new body. At first this body is soft and small, but it will swell with water and increase in size as the shell hardens.
A female horseshoe crab returning to the water at high tide on Plumb Beach, Brooklyn. Photo by Lisa Jean Moore.
Significantly, humans have been able to breed crabs in captivity, but they cannot get them to live beyond their tenth molt—at that time the crabs die instead of surviving through the remaining 6–8 molts and becoming reproductive adults. Scientists do not understand why this might be so.15 Our inability to replicate “natural conditions” for horseshoe crabs means that their reproduction must be primarily studied in the wild. In my experience studying horseshoe crabs when they spawn, there is a great deal of physical contact between humans and crabs. Picking up crabs is relatively simple since they do not pinch, bite, or sting. And they are not too fragile to be handled. As the biologist Mark Botton, one of my key informants, describes them, “They are tough, and ancient, and in many ways indestructible. They are the perfect species to teach undergrads about field biology since they are so easy to catch.” Another of my informants, the esteemed horseshoe crab scientist Jane Brockmann, adds, “What I like about them is that they are predictable. Breeding on the new and full moon high tides makes it pretty predictable. So you can take a class out there and expect to find something.”
My Intellectual Path to Horseshoe Crabs
Sociology, as a discipline, is historically indebted to humanism. In the Western tradition, the human is viewed as the ultimate social/rational/political being: one that is able to perceive the world, think about it, and communicate about that world back to others. The doctrine of humanism affirms the existence of a thinking ego, a self, or an I—the fact that we all share the ability to conceptualize our own respective selves demonstrates a sort of harmonious connection among us, which in turn demonstrates our superiority over all other entities, living and nonliving. For centuries, scholars have explored the role of consciousness and reason as the foundation of our autonomy. We are the only beings who are capable of giving anything meaning or of exerting our influence within the world. Humanism is a vexing philosophy because it is both liberating—freeing us from supernatural explanations over which we have little control—and damning—bogging us down in endless debates about who gets to count as “human.” Sociology has made its business studying
