Environmentalists often condemn migrant species out of hand in the same way that some people condemn migrant humans—and using much the same toxic language. This is lazy thinking. And wrong. The more I looked into it, the more it seemed to me that invasive species might be just the boost that ecosystems messed up by humans often needed. They are often the go-getters, the can-do species that revitalize and reboot nature. They are pretty much the only way nature will cope with climate change, for instance. So demonizing and exterminating them wherever they appear seems like a bad idea.

It turned out I was not alone. I found plenty of “new ecologists” who take the same view. They say we should think of successful ecosystems as dynamic and constantly evolving, with outsider species often the most dynamic elements. Sometimes, I agree, we may want to control aliens because they damage our own activities or offend our aesthetics. But mostly the invaders are good for nature. True environmentalists should be on their side.

BP: What role have humans played in the rise of invasive species?

FP: Nature has always been on the move. Invasions are part of Darwinian evolution—throws of the dice that help ensure the survival of the fittest. But humans have certainly sped this up. You might say we humans are the greatest invader species of all, and we bring plenty of others along with us, whether we are moving crops around the world, or simply carrying species accidentally in ships’ ballast water or cargo holds.

The new arrivals can be very disruptive, especially at first. Look at Burmese pythons, the escaped pets eating their way through the small mammals of the Florida Everglades. But mostly the new arrivals—like human migrants—either fit in or move on. They usually do best in places already messed up by humans, revitalizing hollowed out ecosystems in the way human migrants can revitalize deprived and hollowed out neighborhoods. Even the most successful aliens rarely cause local extinctions. Mostly they leave the ecosystems they invade richer, more biodiverse, and better able to cope with the mess humans create. They are part of the solution, not the problem.

BP: What are some of the most misunderstood invasive species? How are they benefiting their new environments?

Take tamarisk, also called salt cedar, in the American west. Some see this old-world invader as a water-guzzling desert creator. There is a history of water politics behind that false claim that reads like an ecological version of the movie Chinatown. Mining companies demonized the shrub so they could kill it and claim the water “saved.” Gullible environmentalists went along with the story. Actually, tamarisk consumes no more water than local species like cottonwood, but often survives where cottonwood cannot. Tamarisk is holding back the desert. And it is a valuable wildlife habitat, the preferred nesting place for many birds, including the endangered southwester willow flycatcher.

Go to Puerto Rico and you find that alien species like the African tulip tree are the driving force behind a rewilding of the island after farmers who had destroyed the native forests abandoned their fields. The alien trees are reviving soils and providing homes for many birds—both native and alien—that are spreading the seeds of native trees. Without them, the island would still be an ecological basketcase.

Or go to San Francisco Bay, which is widely said to be the most invaded bay in the world. Ever since the Gold Rush, new species have been turning up here in large numbers. There are at least 300 alien species established in the bay, including Amur clams from Russia, Atlantic green crabs, Black Sea jellyfish, Chinese mitten crabs, Japanese gobies, and a sea slug from New Zealand. But this species melting pot is so successful that two years ago, the Ramsar Convention on Wetlands accepted the US government’s designation of San Francisco Bay as a “Wetland of International Importance.” All those aliens must be doing something right.

BP: What recommendation would you give to conservationists who routinely demonize alien species outright?

Don’t take my word for it, but start asking questions about why we use such nasty language about foreign species, and why we would want to go round exterminating them. We wouldn’t do that to fellow humans without giving them a fair hearing, so why do that to other species? Always question the assumption that there is something intrinsically bad about an alien species. If a new alien species suddenly takes hold in your neighborhood, it is probably because the ecosystem is a mess thanks to human activity. By all means attack the root cause. But that is rarely the species itself, which is just taking advantage—and may actually be just what the ecosystem needs to recover. Also, remember that nature is constantly changing, even without human intervention. Change is not bad; it is natural. Too much conservation gets hung up on trying to preserve the past. We should celebrate nature’s dynamism and adaptability a lot more than we do.

About Fred Pearce

Fred Pearce is an award-winning author and journalist based in London. He has reported on environmental, science, and development issues from eighty-five countries over the past twenty years. Environment consultant at New Scientist since 1992, he also writes regularly for the Guardian newspaper and Yale University’s prestigious e360 website. Pearce was voted UK Environment Journalist of the Year in 2001 and CGIAR agricultural research journalist of the year in 2002, and he won a lifetime achievement award from the Association of British Science Writers in 2011. His many books include The New Wild, With Speed and Violence, Confessions of an Eco-Sinner, The Coming Population Crash,and The Land Grabbers.