News | May 21, 2024

Red knots, horseshoe crabs, and us

Conservationist Drew Lanham's call for the care of kinship
J. Drew Lanham looks for birds along the coast at Edisto Island, South Carolina. (Joel Caldwell)


It’s an annual ritual, the flocks of red-breasted shorebirds landing to refuel along the Atlantic shores of South Carolina during one of the longest migrations in the animal kingdom. The red knots’ layover on their journey from the Patagonia region of South America to the Arctic is timed to the spring spawning of horseshoe crabs and the abundance of eggs lining the beaches. But red knots have been less plentiful of late, so much so they are now protected under the Endangered Species Act.

It was the red knots’ dependence on the horseshoe crabs that led SELC and our partners to a historic victory protecting these threatened birds from the harmful impacts of commercial horseshoe crab harvesting. The courts agreed harvesting should be limited because of the vital role crabs’ eggs play in the species’ survival.

The birds’ South Carolina stopover isn’t far from the Edisto-area pink house where J. Drew Lanham retreats for focused writing. A renowned author of books, essays, and poetry, as well as a cultural ornithologist, academic, and MacArthur Fellow, Lanham is intimately familiar with the red knot migration and their reliance on the horseshoe crabs. The following essay dives into his perspective on this prehistoric relationship and the ways our human culture ignores it at our own peril.

(Left) J. Drew Lanham crosses a field scouting for birds. (Right) Dunlins and short-billed dowitchers cruise along the South Carolina coast. (Joel Caldwell)

By J. Drew Lanham

A bird’s-eye view, that’s how I see most of the world. I’m an ornithologist by training and a wild bird adorer by something hard-wired heart-wise. This is to say, I am more than an academically objective identifier of birds. I identify with birds and have been in love with them for most of my life. These lifelong relationships make bonding with them second nature and evoke in me a kind of wild-wishing.

I’m often asked what my favorite bird is, and because answering such a question is impossible, I respond “the one with feathers,” relieved at not having to choose one from ten thousand. I must admit at times to playing favorites though, if only for a moment. That favoritism is torqued by season and habitat. I can’t take a living being out of the context of time and space. Because I love coastal places, especially seashore and salt marsh, shorebirds inspire a certain kind of wandering wistfulness. It is impossible to be in the company of wheeling flocks of them, watching them skitter, scatter, peep, call, and probe, without every sense coming alive as surf pounds the soul and the sulfur stink of pluff mud fills the nose.

The late nature writer and ardent Zen-conservationist Peter Matthiessen categorized shorebirds as “wind birds” and wrote: “The restlessness of shorebirds, their kinship with the distance and swift seasons, the wistful signal of their voices down the long coastlines of the world make them, for me, the most affecting of wild creatures.” I share his soulful sentiments for the fancifully named species like sanderlings, curlews, whimbrel, godwits, willets, plovers, and a robin-sized sandpiper called a red knot (Caldidris canutus). As the ornithological bias often bends my perspective through a featherweight prism, different shorebirds conjure different stories that bind me not just to them, but to other beings not fortunate enough to be feathered. I agree with Matthiessen’s idea of “kinship” but extend it beyond the charm of birds to other beings easily overlooked.

Horseshoe crabs, with their literal blueblood lineage, sit near the head of life’s legacy table at the evolutionary family reunion.

One such kinship tale, the story of the red knots and horseshoe crabs, is a charisma-driven, care-conjuring odyssey that leads me to seek relationship and cause for concern in animals that few see any likeness or relatedness in. Turns out that red knots have a kinship so close to the horseshoe crab that one might consider them cousins of a sort. It is a link that connects us to a kind of ancestral Adam and Eve; the horseshoe crab. Limulus polyphemus is an ancient crustacean evolved in a sea-swamped not-yet-drifted-apart world at the beginnings of life on earth. Being old enough to have crawled from Eden’s seashore gives them ultimate “kin” credibility.

Horseshoe crabs, with their literal blueblood lineage, sit near the head of life’s legacy table at the evolutionary family reunion. The “blood is thicker than water” maxim speaks to family kinship. It’s a saying that falls in a different way on this ancient being that has existed for most of the time that life on earth has existed. After all, finding a horseshoe crab flipped right side down, chocolate brown carapace of armor mired in the sand and its ten spiny legs, water-breathing gills, and exposed undersides drying in the beach sun doesn’t evoke a sympathetic response in many who see it as some odd thing to avoid rather than some elderly ancestor to offer help.

On my wanderings along South Carolina beaches, I come across them mostly in the legs-up, shell-down topsy-turvy state. Forgoing my beach cruising for shells at low tide to enact right-side-up rescue, most of the horseshoes I encounter have been unlucky and long dead, suffocated in dry air. On the occasions when I find one of them still alive but struggling to right itself and return to its saltwater home, I stop not just to observe but to make some kind of difference. Maybe the act will be worth some karmic correction that come’s my way when I find myself turned head down, on the edge of some depression. After all, isn’t helping another in distress the right thing to do?

Ancient history

In these rapidly advancing years, it seems that convergences can be the magic and the miraculous that make life’s journey a sweeter peregrination. I’ve rescued a few horseshoe crabs, but I came to know this species best by its relationship to those wind birds Matthiessen spoke of. Whatever deep-time evolutionary linkages one might attempt to make between the hardshell carapace of Limulus p. and the downy soft feathers, of Calidris c., there is a more observantly obvious and immediately urgent kinship between “crab” and Calidrid.

Imagine living a life on the wind, by wing and feather faith of lift, and muscle powered thrust, to a family reunion scheduled multiple millennia ago.

Each spring, for at least ten thousand years or so but likely beyond that, red knots and their shorebird relatives have come to a time-evolved, moon-mediated agreement with horseshoe crabs. Knot migration to North America coincides with the peak of horseshoe crab spawning. The crab’s reproductive investment in the future provides critical food that fuels the red knot’s journey to the Arctic. The millions upon millions of gravel-like eggs are essential fuel for their journey of almost 10,000 miles from the bottom of the world to the top and back again. Flying north from near Antarctic extremes in South America’s Patagonia or Tierra del Fuego, up past the bulge of Brazil, to island hopscotch through the Caribbean and up the southeastern Atlantic coastline, it is one of the longest migratory marathons. It leads to a reunion that would seem one-sided if the uncountable masses of eggs scattered in the sand could ever be completely devoured by the once abundant masses of shorebirds. But abundance supports abundance in nature and this reunion that crosses blood lines has for a very long time been at the heart of hordes supporting hordes.

A dozen horseshoe crabs are held in a line on a lab table with small tubes drawing light blue blood from them into glass jars.
A large group of horseshoe crabs stretch in a line down the beach.
Horseshoe crabs in the wild contrast vividly with harvested horseshoe crabs in a lab where their blue blood is being drawn. (Ariane Müller


I see humanity in that lineage, linked by flight and wander envy. Sea water is much of who we are, our blood is mostly brine. Horseshoe crabs are eaten by few and have historically been used as fishing bait and fertilizer by others, but now there is a different intensity of threat that humans leverage against nature’s, and their own, best interest.

All those millennia of abundance are being imperiled by an intense bloodlust. Imagine being a red knot, flying all this way to the South Carolina coast through tempest and tumult, past predatory peregrine talons, through a gauntlet of natural barriers, and now those human-constructed. Imagine living a life on the wind, by wing and feather faith of lift, and muscle powered thrust, to a family reunion scheduled multiple millennia ago. It’s a reunion to meet up with an ancient auntie who gives sage advice and provides sustenance too. And then someone somehow abruptly pulls the plug on the show. Red knots, so named because of the rotund nature of their robin-sized bodies made fat by their horseshoe crab egg feast, were choice targets for market hunters, gunners eager to kill not just for their pots, but to feed hungry palates in northern cities like New York and Boston. The knots were easy targets as were many other species of shorebirds and populations plunged in the unregulated and thus unsustainable “harvest.” Fortunately, the Lacey Act of 1903 and the 1914 Migratory Bird Treaty Act came to fruition in the nick of time to stave off the fate that birds like passenger pigeons, Carolina parakeets, and heath hens suffered into extinction. The U.S. Fish and Wildlife Service now lists red knots as threatened, one step away from endangered.

In spite of some protections, oil spills, coastal development and shorelines disappearing under warming, rising seas disrupt and downright destroy habitats and birds. The birds arrive and see what we know, that horseshoe crab populations have dropped. What they don’t know is that it is thanks in large part to demand from the pharmaceutical industry, eager to extract Limulus Amoebocyte Lysate (LAL) from their blue blood. Horseshoe crabs bleed a hemocyanic copper-infused blue green unlike our vertebrate bright red, and it is rich in this protein. LAL can be used in vaccines and to test for potentially fatal endotoxins in humans, though a synthetic alternative exists. This ancient species is literally, and from an evolutionarily figurative standpoint, blue-blooded, and being drained for this same blood.


Become for a moment a horseshoe crab with a lineage that runs millions of years deep. Most of the species that ever existed in earth’s existence have drifted into extinction. You’re a survivor built on a simple plan outlasting trilobites, T. Rex, life-smiting meteorites, Tasmanian tigers, and all life – and the threats to it since. But 21st century humanity’s designs on progress never met a challenge to exploit it could pass up. Never bet against greed. The desire for blue blood threatens you like no crater-creating space rock separating the age of reptiles from the age of mammals could. There’s no denying the need to heal sickness and ease the pain of chronic disease, but doing so at the cost of another species’ existence seems a short-sighted and unethical trade. There’s even less need when science gives alternatives.

The “progress” we put ahead of nature puts both red knots and horseshoe crabs between a shared rock and very hard place. Both in that spot are suffering bruised existences. Red knots, once among the most abundant of shorebirds, have declined so dramatically that seeing them is becoming increasingly difficult.

There’s no denying the need to heal sickness and ease the pain of chronic disease, but doing so at the cost of another species’ existence seems a short-sighted and unethical trade.

We are once again breaking the chain of custody between wild beings and wildness and our own well-being. Use for the greater good might be considered at the noble end of horseshoe crab exploitation, but as a Black man with a lineage of ancestral enslavement behind me, I’ve heard those arguments before. As I spend more and more time in the ACE Basin, one of National Geographic’s Fifty Great Places, and a priceless gem of ecological and cultural convergence where the Ashepoo, Combahee, and Edisto rivers meet, I find a kinship with multiple aspects of my own being. This includes the birds and beasts, the bitter history of a landscape dramatically altered at the cost of human lives considered less-than, and what the future holds for how we all relate to one another across lines of space, time, and identity. That ecological ink blot that helps me understand my relatedness to every other thing is critical for all of us, human skin, rusty red knot feathers, or armor-plated horseshoe crabs.

There is some good news with red knots rebounding after new protections for horseshoe crabs, but these days I advise caution before celebrating. Greed by some who want to exploit nature’s bounty for profit seems to always be a threat. We must be ever vigilant to protect those who can’t protect themselves. Because care is the cause of conservation, and since that care most effectively happens where we draw close to empathy, or at least some sense of personal stake in “saving” nature, I advise thinking beyond human relatedness to expand heart and helping hand to those other beings with whom we ultimately share the same fate.

From somewhere on high, perhaps a migrating red knot looks down and sees me flip a single horseshoe crab that returns seaward. I cannot know what the knot knows, but the bird-lover within knows that helping this ancient uncle return to the sea might mean more eggs spawned on future moonlit nights that will feed shorebirds to give them better chances at surviving and making more of themselves. That means more birds and crabs for us to wonder over and watch. The cause of kinship among us all demands no less.