Burmese pythons can grow to more than 15 ft. (4.5m). They choke their prey with powerful muscles and like to snack on raccoons, rabbits and the occasional small alligator. It is necessary to grab it by its nonbiting end, but this apex predator is easily annoyed and will turn and strike at your hands. Burmese pythons aren’t venomous but their rows of rearward-facing teeth can tear a chunk out of human flesh. Corralling the python requires seizing the snake by the back of its skull. the python then often constricts itself around your forearm, inflating like a blood-pressure cuff.
Native to SE Asia, Burmese pythons began appearing regularly in South Florida more than 15 years ago. It’s likely that pythons brought in as pets had either escaped or were released into the wile, and then – like so many retirees before them – fell in love with the Sunshine State’s tropical climate. Today there may be as many as 100,0000 Burmese pythons living amid the wetlands of South Florida, though no one really knows. Pythons can disappear when they want to, which is most of the time. During a month long state-sponsored hunt in 2013, nearly 1,600 participants found and captured just 68 pythons. Yet scientists have linked a drastic decline in small mammals in South Florida’s Everglades National Park to the pythons, which can lay up to 100 eggs at a time, grow more than 7 ft. in their first two years and now face no natural predators. “Removing a huge portion of all the mammals from the Everglades is going to have a dramatic impact on the ecosystem, but right now, there is nothing that can significantly suppress the python population.
Burmese pythons have proved particularly successful invaders, but they’re hardly alone. On nearly every border, the US is under biological invasion. A quarter of the wildlife in South Florida is exotic, more than anywhere else in the US, and the region has one of the highest numbers of alien plants in the world. While Florida is America’s soft underbelly when it comes to invasives, they are a nationwide problem. There are more than 50,000 alien species in the US, where they’ve often been able to outcompete – or simply eat – native flora and fauna. By some estimates, invasive species animals are the second biggest threat to endangered animals after habitat loss, and one study that invasives could cost the US a much as $120 billion a year in damages. In the Caribbean, lionfish scour coral reefs of sea life; in Texas, feral hogs rampage through farmers’ fields; in the Northeast, emerald ash borers turn trees into kindling; in the Great Lakes, zebra mussels encrust pipes and valves, rendering power plants worthless. On July 1, authorities at Los Angeles International Airport seized 67 live invasive giant African snails that were apparently intended for human consumption.
The problem seems to be getting worse – and we’re to blame. Most invasive species have been brought into the country by human beings either on purpose, in the case of exotic pets or plants, our accidentally, with alien species hitching a ride to new habitats. As gloval trade increases – during any 24-hour period, some 10,000 species are moving around in the ballast water of cargo ships – so does the chance of invasion. Add in climate change, which is forcing species to move as they adapt to rising temperatures, and it’s clear that the planet is becoming a giant mixing bow., one tht could end up numbingly homogenized as invasives spread across the globe. The scale and the rate is unprecedented and has been called “global swarming”. The balance of nature – an ideal state in which every species is in its right place – is seemingly being upended.
Given those fears, it’s no surprise that many conservationists treat invasives as enemy combatants in a biological war. The US federal government spent $2.2 billion in 2012 trying to prevent, control and sometimes eradicate invasive species in an effort that involved numerous different agencies and departments. Yet there’s a small but growing number of biologists who question whether the war against invasives can ever be won – and whether it should even be fought. To these critics, nature has never been balanced, and there’s nothing that makes an alien species inherently bad or a native one inherently good. Human activity has so fundamentally altered the planet that there’s no going back, and we must learn to love – or at least tolerate – what has been called our “rambunctious garden” of a world. The planet is changing, if conservation is going to be relevant, it has to accept that. And that means that the future could look a lot like South Florida.
Life has always been on the move, but until recently that mobility was limited by oceans, mountains and other geographic barriers. That separation allowed life to evolve into as many as 8.7 million separate species, if not far more. But then Homo sapiens arrived. As humans spread around the globe, they brought their favored plants and animals with them, along with stowaways like black rats, which originated in tropical Asia before infesting the planet from the holds of sailing ships.
For a long time there was little concern about the effects of introducing alien species to new ecosystems; they were sometimes even sought after. Thomas Jefferson wrote that “the greatest service which can be rendered any country is to add a useful plant to its culture,” and while he was an envoy in France he sent seeds of grasses, fruits and vegetables to botanists in the US; he even smuggled home native rice from Italy.
In 1871 the American Acclimatization Society was founded to bring “useful or interesting” animals and plants to North America, and the society’s president later released 60 European starlings in New York’s Central Park, part of his dream to introduce every bird mentioned in Shakespeare to North America. He was all too successful: there are now some 200 million European starlings in the US.
It is not surprising that the growth of invasive species has closely followed the growth of global trade. As canoes and clippers gave way to container sips and jumbo jets, it became easier and easier to move species around the globe. In the book The Sixth Extinction, before humans arrived in Hawaii, the islands experienced about one successful invasion every 10,000 years. Now Hawaii gets a new invasive species every month. Even falling political barriers make a difference, during the Cold War, the number of invasive bird species in politically isolated Eastern Europe fell while the number in the free states of Western Europe increased. The sheer speed at which things move around the planet gives them a much better chance to arrive alive, happy and ready to reproduce.
The Great Lakes are one of the most heavily invaded freshwater ecosystems in the world. Since the St. Lawrence Seaway was opened in 1959, oceangoing vessels have been able to sail into the lakes, bringing alien species with them. That’s how the zebra mussel, one of the most tenacious aquatic invasives in the country, found a home in the Great Lakes. Native to southern Russia, the mussel arrived in the ballast water of ships and was discovered in the Great Lakes region in the late 1980s. there are now millions of the mussels in the lakes; clusters encrust anchors and docks and disrupt the marine food chain. Zebra mussels can grow so plentiful that they block the intake valves of power plants and industrial facilities, causing hundreds of millions of damage. The mussels take all the plankton out of the water, pulling out the rug from under entire ecosystems.
As destructive as they can be, zebra mussels are, in the end, mollusks – not the sort of charismatic invader that seizes public attention. But that’s not a problem for the Asian carp. First imported to the South and Midwest by fish farmers in the 1960s and 70s, the Asian carp – a collective name for several related species from China – escaped at some point into the Mississippi River. In the years since, they’ve made their way upriver and are now knocking on the door of the Great Lakes. Bottom feeders, the carp could disrupt the marine food chain if they establish themselves in the Great Lakes, wrecking the region’s $7 billion sport-fishing industry. It doesn’t help that the silver Asian carp have a habit of leaping out of the water when startled by a boat motor, turning themselves into piscine projectiles that can clobber unwary fishermen.
The carp invasion has officials in the Great Lakes region so concerned that they are considering an Army Corps of Engineers plan – one that would potentially cost up to $18 billion – to essentially close the century-old Chicago Canal, cutting off the Great Lakes from the Mississippi River system. Even so, it might be too late. Genetic evidence has been found that some Asian carp are already present in the lakes, although it’s not clear yet whether they are numerous enough to establish themselves.
The reality is that we already live in a deeply invaded world. Look out your window and you’ll see alien species everywhere. Almost all the grasses in American lawns come from somewhere else, including Kentucky bluegrass. More than a quarter of the plants in Vermont and more than a third in Massachusetts come from outside those states. Baseball and apple pie might be American – unless the pies are made from Fuji apples, which were developed in Japan – but honeybees are not. The scientific name – Apis mellifera, or European honeybee – is a giveaway. We are living in a period of the world’s history when the mingling of thousands of kinds of organisms from different parts of the world is setting up terrific dislocations in nature. There’s another name for that terrific dislocation: Florida.
Invasive plants and animals have flocked to Florida for some of the same reasons that more than 600 people a day move there: the sunny climate, the plentiful land and a generally welcoming attitude toward newcomers. And like many of the new human arrivals, invasive wildlife often enter the state through the sprawling hub of Miami International Airport, which ranks first in the US in international freight shipments and live-animal traffic, with about 3,000 live-wildlife shipments every month. While border-control officials check cargo for invasive species, the sheer number of alien specie entering Florida on any given day – and a climate that seems designed to turbocharge the growth of anything living – tilts the odds in the species’ favor. It is ground zero for the impacts of invasive species, and the new invaders are very good at finding new habitats.
Often those habitats are in or around the Everglades, that vast “river of grass” that covers much of South Florida. Half of the original Everglades has been developed for farming or housing, and the sprawling wetland has been carved up by more than 1,400 miles of canals and levees that divert water for South Florida’s 5.8 million people. That mix of suburbs and wilderness makes the Everglades an invasive free-for-all. In the South Dade Wetlands, a small slice of protected territory about 25 miles south of Miami, thickets of Brazilian pepper trees throng the sides of canals, the pepper trees are beautiful, which is why they were imported as ornamentals from South America n the mid-1800s, but they’ve come to dominate more than 700,000 acres of Florida, producing a dense canopy that shades out competitors. It’s one of dozens of invasive plants infesting the Everglades. They outcompete natives and create a monoculture of simpler species where there was once diversity. What kept them in check in their home territory isn’t here.
And that leaves human beings. Florida has spent hundreds of millions of dollars trying to control invasives, work augmented by the efforts of ordinary people, like those who volunteer for the Python Patrol. Begun in 2008 when a python was discovered snacking on endangered Key Largo wood rats, the program has taught hundreds of Floridians to identify invasive snakes and lizards and capture them. It’s not easy work; pythons are ambush predators, waiting out their prey in hiding, and even experts will usually miss 99 pythons for every one they can see in the wild. But training a vast legion of people to spot and capture the pythons is just about the only way to control their numbers. Not that anyone has any idea exactly how many are established in Florida.
Invasions of the Anthropocene. Invasion biology has become a sprawling discipline with its own journals, academic centers and graduate programs. But you can boil it all down to this dictum: the origin of species matter. Just because a plant or animal is alien doesn’t automatically mean it will become a dangerous invasive, but all else being equal, it’s best for nature if species stay at home – and it’s worth spending billions of dollars worldwide to prosecute a war against aliens. No plant is more refined than that which belongs.
To which Mark Davis asks: Who decided what belongs? In 2011, Davis and 18 of his colleagues made waves in the invasion-biology world when they co-wrote an essay in Nature that argued that conservationists should place less emphasis on the origins of a species than on how it acted in its habitat, wherever that might be.
They pointed out alien species like the tamarisk shrub, a drought-resistant plant from Africa and Eurasia that was introduced to the American west in the mid-19th century and eventually condemned as a water-stealing “alien invader”. Becoming the object of a 70-year, multimillion-dollar eradication project. Yet it’s not clear that tamarisks use water at a higher rate than natives, and the plants provide nesting habitat for the endangered southwestern willow flycatcher. The distinction between native and alien species is often arbitrary. The “terrific dislocation” that biologists decried is simply a fact of a globalized, human-dominated planet and is neither good nor bad. It’s just not feasible in the current world to try to garden nature. There is no wilderness, no place that hasn’t been touched by humans.
The Nature article resulted in a swift backlash in the field, including an objection later printed in the journal that was signed by 141 conservation bilologist. It’s like climate change: 99$ of experts will say this is a huge problem that’s getting worse, and then there’s a small fraction who are skeptical.
In truth, though, Davis and his fellow renegades aren’t as far out as they seem. They don’t deny that some existing invasive species – like the emerald ash borer, an insect that has destroyed millions of US trees – are worth fighting or that we should try to prevent invasions in the first place. But they’re right to argue that nativeness in and of itself has little intrinsic value. Native species can cause problems just as alien ones can, as shown by the rising populations of deer and other wildlife in NA, and lien species can sometimes be better adapted to their new habitats than native ones are. In recent years some chefs have even begun to specialize in invasive species, serving up Asian carp as “Kentucky tuna” and offering lionfish sushi. Natives are only those organisms that first happened to gain and keep a footing.
But even though the spread of invasives can actually lead to an increase in local diversity in absolute numbers – North America has an istimated 20% more species now than it did before European colonization – on a global scale, unchecked invasions can lead to planetary homogenization. Just as global trade has allowed megabrands like Walmart and McDonald’s to spread around the world, crushing local mom-and-pop shops, human activity has allowed “super species” like jellyfish and Argentine ants to invade new territory, displacing natives along the way. That’s fine from a purely evolutionary perspective – survival of the fittest and all that. But something will be lost if our planet becomes as homogenized biologically as it is economically and culturally. If we had unlimited resources, we could try to stop this change, but it’s just not possible to do.
Human beings have become the dominant force on the planet, so much so that many scientists believe we’ve entered an entirely new geological epoch: the Antrhropocene. We have already been shaping the planet unintentionally, through greenhouse-gas emissions and global trade and every other facet of modern existence. The challenge now is to take responsibility for that power over the planet and use it for the right ends.-all the while knowing that there is no single correct answer no lost state of grace we can beat back toward.
How we respond to the thickening invasions that we ourselves loosed will be a par to that answer – which is only just. There is one species that can claim to be the most dominant invasive of all time. Form its origins in Africa, this species has spread to every corner of the world and every kind of climate. Everywhere it goes, it displaces natives, leaving extinction in its wake, altering habitat to suit its needs, with little regard for the ecological impact. Its numbers have grown nearly a million fold, and it spread shows no sign of stopping. If that invasive species sounds familiar, it should. It’s us.