Come from away

Do we have a chance against alien species?

Every Easter, while North American children feast on chocolate and marshmallow bunnies, the Adelaide-based confectioner Haigh’s Chocolates offers Australian kids a less menacing alternative: the chocolate bilby, a treat in the shape of a small local marsupial. Haigh’s phased out chocolate bunnies years ago, going “rabbit-free” as part of a partnership with Rabbit Free Australia, a wholly serious non-profit organization whose mission is to rid the country of what it calls its worst vertebrate pest. Rabbits were first introduced by European settlers to Australia in the eighteenth century, to be raised for food, then released from cages for sport hunting. They soon grew to enormous numbers, overgrazing pasture, eating crops, killing young trees, initiating irreversible erosion, and contributing to the decline of many native species. In spite of shooting, poisoning, and trapping, introduced predators such as ferrets, foxes, and feral cats, despite construction of extensive rabbit-proof fence networks, and propagation of rabbit-specific viruses, rabbits still cause $115 million in annual agricultural damage.

Introduced species are a big deal, biologically, economically, and politically, and rabbits are one of myriad transplanted animals and plants that have radically transformed ecosystems on every continent. Programs to quarantine, control, and manage such species cost billions of dollars annually, driven by political decisions too often motivated by a “we have to appear to be doing something” mentality rather than much chance of success.

My own career as an entomologist intersected numerous times with species that arrived from away. These experiences have left me with great respect for the capacity of invasive organisms to spread and thrive, and a healthy skepticism that we have much agency to stop or manage their long-term impact. My first encounter was with the gypsy moth in the early 1970s. As a recent university graduate, I was hired as a temporary employee with the U.S. Department of Agriculture (USDA) in Cape Cod, Massachusetts to develop control methods. Gypsy moths had been introduced to the eastern United States in the late 1800s from Europe by the French astronomer and naturalist Léopold Trouvelot, who was living in the textile town of Medford, Massachusetts, and conducting experiments with silkworms. Trouvelot decided to investigate gypsy moths as a silk-producing alternative, and from this quixotic beginning an invasive-species nightmare emerged. A few eggs blew out an open Massachusetts window, initiating the tenure of what became a devastating forest pest.

Gypsy moth populations in North America quickly reached epidemic proportions, without the predators, parasites, and diseases that control their numbers in their native habitat. These outbreaks are phenomenal; deciduous forests can be stripped of every leaf on every tree for kilometre after kilometre. Excrement drips from trees with the ­persistence of a light rain, and layers of slimy dead larvae that have fallen to the ground make the area around the trees as slippery to walk on as ice.

Our mission was to develop a pheromone-based control program. We had some modest success with the research, although it didn’t turn out to be a game changer in gypsy moth control. The moths remain a major forest pest in the eastern United States and Canada, although outbreaks have become somewhat more manageable through a combination of control measures including pesticide applications, pheromone traps, and introduced predators, parasites, and diseases.

I went on from my gypsy moth days to study honeybees, themselves an introduced species not native to North, Central, or South America. Canadian honeybees were imported originally from Europe, but I began my doctoral studies with African bees that had been imported to South America in 1956 as part of an experiment to breed superior honey producers in tropical climates. Twenty-six swarms escaped, and grew to become what media nicknamed “killer bees.”

The African bees are indeed aggressive, and in addition to wreaking havoc with beekeeping and causing numerous human and livestock fatalities, they were impressive in the magnitude of their success. These bees turned out to be ideally preadapted to New World tropical habitats, and spread quickly and in massive numbers throughout most of Latin America and into the southern United States. They may be the most successful introduced species ever, colonizing new territory at a rate of 200 kilometres per year and growing to unimaginable populations; they now number many hundreds of millions of colonies in the region. The human impact in lives lost and industries threatened also has been notable, with thousands of deaths due to massive stinging incidents, and a major disruption of Latin American beekeeping.

My third intersection with introduced species came in an area in which there is little interest in reversing the invasions: agriculture. Remarkably, 98 percent of North American crops are deliberately imported alien species. In Canada everything from apples (which originated in central Asia) and canola (bred in Canada from rapeseed, first cultivated in India, China, and Japan) to corn (domesticated from maize in southern Mexico) and wheat (first cultivated in the Fertile Crescent) to cows (southeast Turkey) and pigs (many locations in Eurasia) are of foreign origin. I suspect the ecological impact of these farmed plants and animals dwarfs that of the troublesome species we usually think of as invasive. Ironically, invasive insects, weeds, viruses, and fungi plague agriculture, too. The cumulative impact and interaction of invasive species cause annual crop losses in the United States of US$120 billion.

Leslie Anthony’s book The Aliens Among Us is the latest in a litany of books that shock us with lurid stories of ecological transformation and economic devastation, then provide justification for robust programs to deter future arrivals, eliminate new infestations, or manage established species. Anthony, a British Columbia–based writer and biologist, has a tremendous set to choose from, but one of the more useful aspects of his book is that many of his examples are Canadian, some of them quite dramatic.

One example are the zebra mussels introduced into the Great Lakes in the mid 1980s, initiating a cascade of ecosystem changes. Each plankton-feeding mussel produces up to a million eggs annually, consuming all the organisms and particulate matter from about a litre of water a day. Collectively, they turned Lake Erie from turbid to clear, essentially a biotic desert. The clear water allowed the aquatic plant Eurasian milfoil to bloom, as well as blooms of blue-green algae, that led to downturns in the population of a fish related to the herring: the alewife, yet another invader. Alewives had become the major food source for lake trout and introduced Pacific salmonids, which then also declined.

Earthworms are one of Anthony’s unexpected Canadian invaders; native North American species reached only as far north as just below Chicago. But settlers introduced European earthworms that thrive considerably farther north, perhaps accidentally bringing them into Canada in soil used to protect imported plants. These exotic worms are slowly rebooting Canadian soil, with unknown consequences for the bacteria, fungi, and plants that evolved in a biota without them.

Two other surprises in the pantheon of introduced Canadian species described by Anthony are moose in Newfoundland and deer on Haida Gwaii. Both are native to Canada but weren’t found on either of these islands until recently, brought in by European settlers to provide something to hunt. Both populations exploded and they became pests, the moose severely inhibiting forest regeneration and timber regrowth as they browsed, while also becoming a danger on Newfoundland highways. Deer on Haida Gwaii have threatened the native cedar forest and impacted the cedar-based cultural heritage of the Haida Nation as they consume the tender shoots of newly sprouted cedar trees.

Anthony covers economics and efficacy of control, which usually summarize into one basic story: very expensive, with only scattered success. Control of sea lampreys in the Great Lakes, using physical barriers to prevent lampreys from going up rivers to spawn, as well as a chemical that’s lamprey-specific, costs US $50 million per year, yet they keep coming back.

And controls can themselves be harmful. Managing the towering Japanese knotweed usually involves spraying glyphosate, commonly known as Roundup, a highly controversial herbicide under constant review by regulatory authorities for its carcinogenic and antimicrobial qualities.

The raw material is here, then, for an excellent book, but The Aliens Among Us suffers from its verbosity; the book would have been considerably more effective if it were a third shorter, and if Anthony’s sentences and paragraphs were better organized. And, while populating a book about invasive species with the human characters associated with their control is usually a good way to make science writing more accessible, Anthony provides too big a cast of characters, and doesn’t always have a good eye for compelling personal stories.

Perhaps the most interesting moment in Aliens pops up almost as an afterthought, at the very end of the book, when Anthony introduces the word “solastalgia,” meaning “psychic or existential distress caused by environmental change.” I had wondered what impelled Anthony to write this book cataloguing species under attack and in decline, but that word, solastalgia, suggests Aliens can best be understood as a long prose poem expressing the distress of someone clearly at home in the outdoors seeing the recognizable vanish during his lifetime.

Beyond the innumerable stories of ecological change and economic and management challenges caused by invasive species, there is this: The natural world is increasingly disrupted, losing its familiar character, challenging our sense of stability. “Familiar” is a highly relative term, of course, and the idea of “native species” is particularly fluid. What is clear is that non-native species, whether introduced deliberately or accidentally, have distorted habitats across the globe. The natural environments we know today are not the ecosystems our parents or grandparents would have recognized. This has been true ever since humans began migrating out of Africa, but the pace has accelerated.

What is native, and what belongs, is an artifact of historical memory. Each panicked quarantine, eradication, and control program is justified by benefits to particular industries and attempts to protect ecosystems, but the familiar becoming unfamiliar may be the least appreciated driver behind our concern about alien species. There are few dramatic success stories with eliminating or controlling introduced species as we exert massive effort to pull out weeds, kill mussels, cull moose, or build pricey barriers to keep out fish. What usually occurs is that the aliens wreak havoc, they evolve and we adjust, ecosystems change, management is moderately successful, and their presence becomes the new normal. Eventually normal becomes native.

The Aliens Among Us certainly highlights that there’s good reason to feel solastalgic, with our planet’s environment changing as dramatically as it has been in recent decades. The most inescapable conclusion from Anthony’s book may be the hardest to accept: The aliens are among us, and they are here to stay.