How Migrating Crabs Help Us Rethink Our Roads

10.16.2023

What does it mean for a highway merely to visit a landscape, rather than to dominate it?

Every year, the remote Colombian island of Providencia hosts one of nature’s strangest, grandest phenomena: the mass migration of black crabs. Legions of crabs, each roughly the size of a deck of cards, scuttle between forests and beaches to spawn, crossing roads in such numbers that the ground appears paved with their chitinous bodies. This would seem a recipe for mass roadkill, but, as Atlas Obscura reported in 2018, Providencians take extreme measures to prevent crab flattenings. The military’s “crab watch division” shuts down some roads to vehicle traffic, and drivers elsewhere veer to avoid the wandering crustaceans, a maneuver so widespread that islanders have a name for it: “crab swerving.”

Elsewhere, most interactions between roads and wildlife don’t end so happily. Our planet is enmeshed by some 40 million miles of roads, a network whose ecological impact is almost incomprehensibly vast. Walls of traffic prevent animals from migrating and mating; the whine of engines and tires repels songbirds from swaths of habitat; chemicals in tire particles kill salmon. And then there’s roadkill, the highway’s most direct and conspicuous harm, which claims more than a million vertebrate victims per day in the United States alone. It isn’t only common critters, like white-tailed deer and gray squirrels, that are afflicted. For vanishingly rare species like Iran’s Asiatic cheetah, cars pose a true existential threat.

Roads are especially pernicious because they don’t merely annihilate nature—they separate us from it. Perched in our sealed vehicular bubbles, we are effectively insulated from our surroundings, which tend to smear into a monotonous gray-green blur. Roads, and the high-speed travel they facilitate, also conceal their own crimes: You might notice the dead deer on the shoulder as you race by at 70 miles per hour, but you’re almost certain to miss the smushed toad or battered sparrow. Even the perspective from which we view roadkill reinforces our disregard for it. Whereas zookeepers prefer to design enclosures that present animals at or above visitors’ eye level, for fear that “visitors who look down at zoo animals… are more likely to subconsciously perceive them as subordinate beings,” cars hoist up their drivers like royalty upon thrones, towering high above lowly carcasses.

Even as roads obliterate nature, however, they paradoxically connect us with it.

Even as roads obliterate nature, however, they paradoxically connect us with it. Roads are primarily how we experience national parks and forests, “windshield wildernesses” that Americans nearly always visit by car. Certainly you can dispute the wisdom of injecting millions of vehicles into ostensibly protected areas, but it’s hard to deny that automotive tourism has also developed a constituency for the conservation of these special places. Cars are at once catastrophic for wild animals and the intermediaries through which we meet them. Years ago, driving in a California park on a damp evening, I felt an eerie premonition. This would be a good time to see a bobcat, I told my wife. Moments later, the prophesied bobcat appeared, trotting through our high-beams. The cat herself surely wasn’t eager to interact with our Camry, but it was a strange and surreal encounter, one facilitated by a car.

As crab-swerving Providencians illustrate, it isn’t inevitable that our vehicles separate us from the natural world. Our general heedlessness notwithstanding, many societies have developed traditions that honor the animals who scurry across our highways. In the course of reporting my new book, Crossings: How Road Ecology Is Shaping the Future of Our Planet, I had the chance to explore some of those cultures. In the Australian state of Tasmania, I met animal rehabbers, or “carers,” who rescue car-orphaned wombats and wallabies and, at great personal expense, raise them to adulthood—a form of reparations for the damages that cars inflict. In Oregon, I joined a group of volunteers who scoop up migrating frogs in buckets and carry them across roads to their breeding wetlands, a vernal rite practiced by thousands of amphibian chaperones in countries as far flung as Canada, Belgium, and South Africa. I spoke with some of the many Americans who harvest roadkill for food, and even ate highway-sourced elk myself—a tribute to the lives that our automotive culture takes.

These examples, granted, are few and imperfect. What we need, in the end, is more ecologically sensible infrastructure: roads that connect rather than divide. We might take a cue from Montana’s Confederated Salish and Kootenai Tribes, who, in the early 2000s, objected to a state proposal to widen the highway that runs through their land. A faster, busier highway, the tribes reasoned, would destroy the elk, deer, bears, and other animals fundamental to their culture. “The road is a visitor,” the tribes wrote, that ought to “respond to and be respectful of the land.” When the state finally rebuilt the highway, it included 41 wildlife crossings: tunnels, underpasses, and a bridge that have collectively allowed thousands of animals to safely navigate the road. The highway may not be ecologically benign—no road truly is—but at least it attempts to harmonize with the landscape’s inhabitants rather than bludgeoning them.

What we need, in the end, is more ecologically sensible infrastructure: roads that connect rather than divide.

In the course of working on Crossings, I encountered a few other examples of roads that aimed to be visitors rather than destroyers. In Brazil, home to a thriving road-ecology movement, I drove a highway that runs through a state park near São Paulo. Every night the highway closes to protect animals, and it’s designed to thwart high speeds: It winds sinuously through the forest, crimped by frequent hairpin turns, and rises and falls like a gentle rollercoaster. This is a road that forces its passengers to drive at a leisurely pace and pay heed to their surroundings—a subversive choice in a world governed by speed. The roadkill historian Gary Kroll has written that the only path toward dampening the destruction of the Anthropocene is by forcing “the deceleration of industrialized humans”; here is a road that radically decelerates drivers.

Other road managers have taken the similarly progressive approach of slashing traffic altogether. In Denali National Park, where private vehicles are generally prohibited from most of the central park road, I hopped on a bus and rode it 50 miles through the mountains and tundra. Whereas many parks, like Yellowstone, are clotted with cars, the relative infrequency of Denali’s shuttles allows sheep, bears, and other animals to migrate safely during prolonged gaps in traffic. And, by compelling visitors to take the bus together, the park turns tourism from a solitary experience into a communal one. The Denali bus system unites its riders in the common pursuit of spotting caribou, ptarmigan, and other creatures, joining humans with nature and each other rather than disconnecting us.

When mass transit is impracticable, wildlife crossings are our best option. Remarkably, Providencia isn’t the only island blessed with a spectacular migration of crabs. There’s also Christmas Island, an Australian territory where tens of millions of red crabs traipse seaward in October and November—and, like so many wild animals, get crushed along the way. But the island’s crabs aren’t without recourse. In 2012, the government installed its first “crab bridge”: a catwalk-like overpass, flanked by fencing, that carries the clawed hordes safely across a busy road, no crab swerving necessary. Now, rivers of crabs course over the bridge every year, a glorious spectacle that tourists and locals flock to witness (not to mention watch on YouTube). The road may not truly be a visitor to Christmas Island—some crabs, inevitably, are still crushed—but, thanks to the crab overpass, it isn’t a conqueror of the land, either. It’s a road that accounts for its wild users as well as its human ones, a road we share.