Accidental hobos, exotic species travel with us everywhere. A list of known invasive species would fill pages, and their handiwork volumes. Because, like the Burmese python, they can wreak havoc with an ecosystem, we scorn them as marauders, as if it were their fault. But most often we’re the ones relocating the planet’s life forms.
Invasive species may carry hobos of their own, contagious ones we’re not immune to. When a San Francisco woman’s pet boa, Larry, fell ill recently, scientists studied the genome of boas and to their shock discovered a genetic mishmash of arenaviruses, which spawn such human nightmares as Ebola, aseptic meningitis, and hemorrhagic fever. It’s entirely possible, they surmise, that Ebola began in snakes and spread to humans. Or that, somewhere along the evolutionary road, snakes became vulnerable to Ebola, just as we did. Now we know that reptiles can harbor some of the world’s deadliest human viruses, yet we still ferry them from one locale to another.
Pythons aren’t the only brawny Floridian invaders. In Cape Coral,
monitor lizards—which can reach six feet long—threaten the protected, and altogether winsome, burrowing owl. Gambian pouched rats are overrunning Grassy Key. Cuban tree frogs devour smaller native frogs. Giant African snails dine on five hundred different plants. Jumbo green iguanas are driving the Miami blue butterfly toward extinction. And monk parakeets flock across the Florida skies, flat-nosed as aging prizefighters, making otherworldly shrieks that sound like people prying the lids off cans of motor oil. Unfortunately, their large colonial nests can damage residential trees and electrical power lines, and not everyone is a devotee of squawks, so they’re regarded as a nuisance. Florida boasts more invasive species than anywhere else on Earth, from wild boars and Jamaican fruit bats to squirrel and vervet monkeys, nine-banded armadillos, and prairie dogs.
The same thing can happen in freshwater, and the Finger Lakes now teem with zebra mussels (Russian natives) that clog boat engines and water intake pipes and weigh down buoys. In Tampa Bay, green mussels (New Zealand natives) are smothering the local oyster reefs. Asian carp are turning the Great Lakes into their private dining room. With great relish, the rainbow-sheened Japanese beetles are snipping rose leaves into doilies. Although the Nile perch was introduced into Lake Victoria to appear on the tables of locals, no one counted on its predatory gusto, and it’s decadently feasting on a hundred species of native fish.
We’ve been wantonly shuffling life forms for tens of thousands of years. Migrating bands of
Homo sapiens
carried plants, animals, and parasites with them on their travels, and ancient texts often speak of importing exotic delicacies and species from foreign lands. Vagabond species travel in our luggage, cuffs, and cars—shadowing us around the block and around the world. During the seventeenth- and eighteenth-century voyages of exploration, along with ideas and goods we spread vermin and disease. We colonized every continent and all but the most extreme ecosystems, reconfiguring them at speed. Just breezing through our
lives—hiking across a meadow, commuting to work, flying or sailing overseas—we keep rearranging nature like a suite of living room furniture.
So invasive species have been running riot for ages, some a plague and a nuisance, others a delight. We’ve transplanted a great many plants and animals on purpose, for their beauty, novelty, taste, or usefulness—from starlings and poison ivy (a nonallergic European found it pretty and took it home with him) to exotic reptiles and azaleas. Charmed by the climate and organisms at their new locale, they’ve taken hold, sometimes fiercely (as is the case with eucalyptus, bamboo, and Indian mongooses), to the distress of local species and human residents. People love their English ivy, Norway maple, bullfrogs, Japanese honeysuckle, oxeye daisies, St. John’s wort, dog roses, Scots pine, etc. In contrast, such alien invaders as African bees, tiger mosquitoes, fire ants, water lettuce, burdock, lampreys, loosestrife, bamboo, kudzu vine, and dandelions (which apparently accompanied pilgrims on the
Mayflower
) are scorned, cursed, and uprooted.
We insist that invasive species don’t belong in wilderness, but native ones do—even if they’ve died out. Inspired by that notion, we’ve reintroduced wolves into Yellowstone, moose into Michigan, European lynxes into Switzerland, musk oxen into Alaska, Przewalski’s horses into Mongolia and the Netherlands, red kites and golden eagles into Ireland, cheetahs into India, black-footed ferrets into Canada, brown bears into the Alps, reindeer into Scotland, northern goshawks into England, Bornean orangutans into Indonesia, condors into California, giant anteaters into Argentina, Arabian oryx into Oman, peregrine falcons into Norway, Germany, Sweden, and Poland—and a great many more. At the same time we’re destroying some ecosystems, we’re busy recreating many others.
People may talk about rebalancing an ecosystem, but there is no perfect “balance of nature,” no strategy that will guarantee perpetual harmony and freedom from change. Nature is a never-ending conga line of bold moves and corrections. Hence the continuing debate about whether or not the Everglades should be python-free
or allowed to evolve into whatever comes next. Ever since the 1920s, we’ve been transmogrifying Florida swamps into houses. So the real question is what sort of pocket wilderness we prefer.
I’m of two minds about this case. On the one hand, I don’t want to disturb the dynamic well of nature. Habitats keep evolving new pageants of species, and we shouldn’t interfere. Yet I also sympathize with those who argue that we should capture the pythons in the Everglades and allow the ecosystem to return to its admittedly idealized state, where foxes, rabbits, deer, and a host of other vanishing life forms may flourish. We’re losing biodiversity globally at an alarming rate, and we need a cornucopia of different plants and animals, for the planet’s health and our own. By introducing just one predator into a beloved habitat, we’ve doomed a shockingly large segment of species and all those that depend on them.
The tug-of-war we secretly feel between our animal and human natures is part of what makes us endearingly compassionate, and mighty strange primates. Unlike other animals, we care deeply about scores of life forms with whom we share the planet, even though they’re not family members, not even species members, for that matter, not possessions, and not personal friends. We care abstractly about whole populations we may not have seen firsthand, determined to help fellow creatures survive. We feel a powerfully mingled kinship.
Whatever interventions or restorations we might plan, our unplanned intervention, in the form of climate change, is rearranging habitats in ways we can’t begin to control, spawning migrants everywhere. We may notice more pine or spruce beetles this year, or fewer familiar butterflies poised like pocket squares atop the flowers, or thinner fire-crisped forests with dusty winds and jaw-dropping heat. We may wonder where all the slender-necked corncrakes have gone. We may obey the rules and not water lawns or wash cars or let the faucet run while brushing teeth. But we may not connect the dots and link less water and missing butterflies and corncrakes to early spring and snowpacks melting too soon, leaving little water for
parched forests during the long torrid summer, when already weakened trees face an armada of beetles and incendiary drought.
This is not so much a vicious cycle as a carelessly torn fabric. You notice a ripped seam, and though you may procrastinate about fixing it, it annoys your senses, it picks at your awareness, something isn’t as whole. The foxes have moved north, there are new snakes in the yard, field mice have either waned or multiplied to Pied Piper of Hamelin status, West Nile virus is slaying the local crows, and you spotted something long with eyes and scales swimming in the canal. Lured by the warmer, north-spreading swamps, alligators have begun slithering up from Florida into North Carolina. In time, they may well become native to Virginia, maybe venturing as far as Virginia Beach, with some trailblazers swimming up the Potomac to D.C.
One keystone species, plankton, at the heart of the ocean food chain, tells a tale of the changing times. Tiny shrimplike flagellates in the trillions, without a thought among them, they’re barely visible to us and seem far too weak to act as a keystone, without which hazel-waved ocean life would collapse. But they are one of the largest biomasses on Earth, drifting everywhere on the currents like pointillist clouds.
In Arctic waters, where polar bears travel the corridors of sea ice with their young, resting and hunting, and seabirds nest on icy cliffs, flying to fish through cracks in the ice, seals give birth and raise their young atop the floes. Walruses ride on magic carpets of ice to fish farther afield. With warmer water, there are fewer icebergs where algae cling, and fewer algae-eating plankton as a result. According to a recent study published in
Nature
, worldwide levels of plankton are down 40 percent since the 1950s, which means less food for the plankton-feeding fish, birds, and whales.
Less plankton leads to fewer krill, tiny crustaceans whose numbers have also plummeted, and fewer petite Adélie penguins, which feed on krill and squid in Antarctic waters at the other end of the globe. Untidy masons of the penguin world, Adélies build nests of
stones along gently sloping beaches and raise fluffy, brown, yeti-shaped chicks in those miniature craters. When I visited one large, squawksome colony twenty years ago, stones were a precious commodity. But, according to the ornithologist Bill Fraser, that Adélie population has dropped by 90 percent in the past twenty-five years. With so few couples courting, there are stones abounding, but less food for the orcas (killer whales) and leopard seals that prey on the penguins.
Yet the Anthropocene (like nature itself) rarely tells simple stories. In Alaska, our bestirring of the weather is good for the nearly extinct trumpeter swans, who are using the longer summers to feed and raise their young. Orcas will also profit from the warmer waters. As Arctic seam ice shrinks to a record low, undulating orca shipping lanes open up across the pole via the once-fabled Northwest Passage, changing the ecology of the northern ocean. The melt allows the orcas to widen their range and catch more of the white “singing” beluga whales, the canaries of the ocean, and the unicorn-tusked narwhals, two of the orca’s favorite meals. But both the belugas and the narwhals are endangered.
How astonishing it is that just one warm-blooded species is causing all this commotion. Creating hives of great megacities and concrete nests that tower into the sky is impressive enough. But removing, relocating, redesigning, and generally vexing and bothering an entire planet full of plants and animals is another magnitude of mischief beyond anything the planet has ever known. The first is just brilliant niche building, something other animals do on a much more modest scale. For instance, beavers fell trees and dam up streams to create ideal ponds for their underwater huts, and in the process some flora and fauna are dislodged. But no other animal widens its niche to disturb every life form on every continent and in every ocean.
The addled climate is boosting some species and harming or extinguishing others, and not in faraway places, but close to home, in signposts as plain as the jamboree of Canada geese on your lawn.
This news of climate change isn’t accusatory, jargon-ridden, arguable, or even verbal. It’s local and personal when eagerly awaited butterflies—the ones that captivated your parents, you, and your children every Good-Humor-jingling summer you can remember—have fled. Some things are more visible in their absence.
In England, the once-rare Argus butterfly has been extending its range northward over the past thirty years, and altering its diet in habitats free of its natural enemies (parasitoids). It’s a marvel with brown wing tops fringed in white, and bright-orange eye dots; the underside is paler brown with black and white eye dots plus the orange. The North Country nurse, leaving her local pub, won’t see her favorite winged pub-crawlers flitting across the meadows. Until she visits her sister thirty miles farther north, where the rare beauty is now plentiful.
How come you now get the butterflies and I don’t?
she may be thinking with a touch of sibling eco-rivalry. Parasitoids used to finding Argus caterpillars on certain plants haven’t kept up with Argus’s northward migration.
Imagine if you woke up one morning and discovered that the restaurants across the street, the nearby deli and groceries—in fact, all your usual food pantries—had moved several hours north during the night. Would you make long tiring shopping trips, change your diet, or follow the food and resettle in the north? Like our hunter-gatherer ancestors, you’d probably pack up and follow the herds. (Our herds may lie motionless on shelves these days, but we’re still out there hunting and gathering.)
The Spanish ornithologist Miguel Ferrer estimates that around twenty billion birds of many species have altered their migration pattern because of climate change. “Long-distance migrators are traveling shorter distances; shorter-distance migrators are becoming sedentary,” he reported at a conference of two hundred migration specialists. “The normal summer temperature in your city twelve months ago is now normal four kilometers further north. It doesn’t sound like a lot, but that’s twenty times quicker than temperatures changed in the last ice age.”
An Audubon Society study found that roughly half of 305 species of North American birds are wintering thirty-five miles farther north than they did forty years ago. The purple finch is wintering four hundred miles farther north. Birds are fun to watch and beautiful, of course, but they’re also essential pollinators, seed dispersers, and insect eaters whom we need to help crops and ecosystems flourish.
It’s not always easy for birds to migrate in our citified, fragmented landscapes. Some species, fooled by warm weather into traveling too early, arrive in new environs before the food is sprouting in the fields. Once upon a time corncrakes filled the skies from northern Europe to South Africa with long-necked speckled charm and hoarse calls, nesting in field edges, or in dense vegetation and grasslands. As we’ve mown those fields to plant crops, corncrakes have lost their foothold and become scarce. Fortunately, through the synchronized efforts of fifty countries, from Belarus to Tasmania—such tactics as asking farmers not to mow their grasslands until after the chicks have fledged—corncrakes and their tottery black young are making a comeback.