Not all invasions come from marauding armies. You can devastate a place just by introducing a non-native species that creates dramatic and unexpected shifts in the dynamics of the ecosystem.
It's no coincidence that we refer to non-native species that begin taking over a new environment as "invasive" — when the local environment is ill-equipped to handle the new species, it can lay claim to every resource it can access and hurt countless native species in the process.
Here are ten examples of non-native species that quickly became an enormous, invasive problem.
In The War of the Worlds, H.G. Wells provides a frightening description of a world overcome by an invasive species of Martian plantlife called simply "the red weed":
Next day, the dawn was a brilliant fiery red, and I wandered through the weird and lurid landscape of another planet, for the vegetation that gives Mars its red appearance had taken root on Earth. As man had succumbed to the Martians, so our land now succumbed to the red weed. Wherever there was a stream, the red weed clung and grew with frightening voraciousness, its clawlike fronds choking the movement of the water. And then it began to creep like a slimy red animal across the land, covering field, and ditch, and tree, and hedgerow, with living scarlet feelers.
The invasion of an alien species that dominates life on Earth has since become a common trope in SF and fantasy, but it happens in real life too. Here's our list:
Also known as the "mile-a-minute vine" and "the vine that ate the South," the Kudzu vine is native to Japan, but was first brought to the United States in 1876 when it was featured at the Philadelphia Centennial Exposition as a hardy, fast-growing vine that could help inhibit soil erosion. What they failed to mention at the Exposition was just how fast they meant when they said Kudzu was "fast growing." Since its introduction, Kudzu has been spreading across the U.S. at a rate as fast as 150,000 acres annually, due primarily to the fact that its individual vines can grow upwards of a foot per day in the right conditions, as the seasonal photos of this house (via) help illustrate.
9) The Black Rat
The black rat is most likely one of the first invasive species to ever be inadvertently distributed by humans. The species originated in tropical Asia, but is believed to have reached Europe by the first century A.D. before spreading across the world, hitching rides en masse on European ships. Since then, the black rat has thrived in just about every region of the world, and has adapted exceptionally well to rural, urban, and suburban environments alike. Unfortunately, its success as a species, in combination with the success of numerous other species of rats, is believed to have come at the expense of dramatic population declines and even extinction of countless bird, reptile, and other small vertebrate species the world over.
8) The Asian Tiger Mosquito
This Asian tiger mosquito is characterized by its distinctive black and white stripe pattern, and while it's native to tropical and subtropical areas of Southeast Asia, scientists believe it has quickly become one of the planet's most widely-distributed animal species, spreading to at least 28 countries outside its native range in the last two decades alone. The tiger mosquito is believed to be spread through — of all things — the international tire trade, as tires stored outside tend to retain rainwater, and provide the ideal breeding and living conditions for the mosquito. It poses a distinct threat to populations worldwide, not only because it carries viruses like Dengue and West Nile, but because it tends to associate closely with humans, and is known to feed 24 hours a day (many species of mosquito only feed at dusk and dawn).
7) The Cotton Whitefly
The cotton whitefly is living proof that some of the most hard-hitting invasive species come in tiny packages. Adult whiteflies measure just a millimeter long by the time they reach adulthood, but are known to feast (in staggering numbers) on 900 different kinds of plants worldwide, and are capable of transmitting upwards of 100 different plant viruses. While whiteflies are believed to have originated in India, you'll find them thriving on every single continent but Antarctica. (Image via)
6) The Snakehead Fish
The snakehead is an absolutely nightmarish animal. In fact, National Geographic went so far as to nickname the Northern Snakehead "Fishzilla," and with good reason. Snakehead fish are a veritable force of nature — they have sharp, shark-like teeth; an appetite for for blood; can grow to over three feet in length; can lay up to 75,000 eggs a year; and can even breathe and migrate on land, searching for other bodies of water for up to four days at a time through the use of a primitive breathing organ.
While they were originally native to East Asian waters, various species of snakehead have decimated native food chains in the US ranging from Maine to California. (Image via)
5) The Asian Longhorned Beetle
The Asian longhorned beetle actually spends the most destructive period of its life in a larval stage, during which time it tunnels and feeds on the layer of trees found between their bark and their wood. In large enough numbers, these larvae can eventually kill the tree. To prevent new infestations, officials often must resort to cutting down and burning infested trees.
Originally native to countries in Asia like Japan, infestations of Asian longhorned beetles were first detected in New York around 1996, but quickly spread to the majority of the East coast, where they are estimated to threaten 30-35% of trees on the Atlantic coast's urban areas. They're also found in California, Ontario, and parts of Europe. The economic toll of the Asian longhorned beetle is estimated to number in the tens to hundreds of billions of dollars.
4) The Burmese Python
The Burmese Python provides the perfect example of what can happen when a large, predatory species is introduced into an environment where the native wildlife offers little-to-no competition for resources. The huge snakes — which can grow to upwards of 20 feet in length — are native to the tropic and subtropic areas of Southern Asia, where they are just as at home hanging out in and around water as they are slithering around in the treetops. Their accidental introduction to the wild in Florida, however, has shown that the species also does particularly well in the semi-aquatic environment of Everglades National Park, where an estimated 30,000 Burmese Pythons have made a habit of feasting on a variety of endangered birds and alligators (yes, alligators). (Image via)
3) The Cane Toad
Sometimes invasive species are introduced into regions as a form of biological pest control. Sometimes these non-native species actually do a pretty good job of handling the initial pest problem. And sometimes they do such a good job that they become an enormous pest problem themselves. The cane toad is often cited as the perfect example of an introduced species gone horribly wrong. The cane toad is native to South and Central America, but when its introduction to regions of Hawaii, the Caribbean, and the Philippines to fight pests in sugarcane fields yielded impressive results, it was quickly imported to various other regions worldwide.
Unfortunately, cane toads have a nasty habit of not just eating crop pests and insects, but also just about any terrestrial animal that they can fit their grotesquely huge mouths around — which is saying something, given that they can grow to over 30 cm in length. They also secrete toxins capable of killing just about any animal they come in contact with (humans have died after ingesting their eggs), meaning that they tend to be seriously lacking in the natural predator department. (Image via)
2) The European/Common Rabbit
The common rabbit is native to southern Europe and north Africa, but the tendency for rabbits to... overproduce... has led to their introduction and unchecked expansion on just about every continent but Antarctica and Asia. The most famous case of population explosion probably occurred in Australia, where, in 1859, an English farmer by the name of Thomas Austin introduced just 24 grey rabbits to his plot of land to remind him of home; Austin surmised that "the introduction of a few rabbits could do little harm and might provide a touch of home, in addition to a spot of hunting."
Within ten years, however, the rabbits had bred with local rabbits on such a prolific scale that two million could be shot or trapped annually without having a noticeable impact on the population. By 1900, the rabbit population had exploded to a size reflective of an almost exponential population growth, had contributed to serious erosion of soils across the continent by overgrazing and burrowing, and are believed to be the most significant known factor for species loss in Australia's history.
1) The Nile Perch
The Nile Perch is native to a number of freshwater African lake and river systems. When it was introduced to Lake Victoria in the 1950's however, the lake's ecosystem was not prepared for it. While populations of the fish were kept in check through commercial fishing for several decades, the population exploded in the late 1980's, leading to the extinction or near extinction of several hundred native species. The devastating impact of the gigantic fish — which can grow up to 2 meters in length and weigh in at over 200 kg — is believed to be the result of its voracious appetite for key ecosystem-supporting members like fish, crustaceans, insects, and zooplankton. (Image via).
Plant and Animal species on this list were selected from The Global Invasive Species Database
For more information on invasive species in the U.S., visit the USDA Animal and Plant Health Inspection Service
Top image of Red Weed by NikeDorchain at deviantART