In a time when the threat of a sixth mass extinction looms ominously over the planet, most scientists are working hard to save as many species as they can. But there are some experts out there who are actively trying to kill off certain animals — and, according to them, they're doing it for the good of the Earth.
Welcome to the fight against invasive species — species that aren't native to a region but somehow got introduced to the area and managed to stick around and really mess things up.
The thing that really makes an animal "invasive" and not just "non-native" is that it wreaks havoc on the local ecosystem, either by attacking native species, out-competing them for resources like food and habitat space, or just changing the native landscape in a way that hurts the local flora and fauna.
Invasive species can get introduced in all kinds of ways. Some are accidentally carried over on ships from other countries. Some started out as exotic pets, which got loose and successfully bred more generations in their new environment. Even climate change can play a role in the spread of invasive species, allowing some animals to expand their range to new areas that previously weren't warm enough to support them.
Invasive species are a problem all over the world. The US alone is currently home to dozens of invasive plants, animals, and even microbes. The problem is so concerning that President Bill Clinton signed an executive order in 1999 creating a National Invasive Species Council, which keeps tabs on invasive species in the country and drafts management plans to deal with them.
We've selected some of the world's worst offenders to highlight. Here's how they got here, how they're messing with the local ecosystems, and what scientists are doing to try and stop them. While we don't want to make these animals extinct, they definitely need to be controlled or completely removed from some areas of the globe.
Burmese python
The Burmese python is the poster child for the dangers of the exotic pet trade. These animals were originally imported from Southeast Asia as pets. Inevitably, a few escaped and went on to pretty much take over the Everglades.
It's no joke — Burmese pythons have really taken to life in southern Florida. The snakes eat basically everything, and a few have even been found with alligators in their stomachs.
Florida's National Park Service has employed an aggressive eradication campaign for years, and claims to have removed more than 2,000 pythons from the area since 2002 — but it's not enough.
Experts believe this number is just a fraction of the population that now exists in the park, and it's likely that the pythons will never be completely eradicated. But efforts to keep their numbers down may be helpful in making sure the snake doesn't totally destroy the Everglades' unique and fragile ecosystem.
Wild boar
The wild boar has been in the country since the 1500s and was originally imported from Europe as a food source. It's now widespread across the Southern United States and in California. According to the US Department of Agriculture (USDA), there are now at least 5 million wild boars in 35 states, with the biggest populations in California, Oklahoma, Texas, and Florida.
According to a 2007 report from Portland State University, wild boars can cause a lot of damage to local ecosystems by eating native plants and by rooting in the dirt, which can erode soil, tear up native plants, and even make room for invasive plant species to move in.
In states with established boar populations, the USDA's goal is to suppress populations enough to stop them from causing so much damage. In states with low or emerging populations, the goal is elimination.
Hunting the hogs is a simple control tactic employed in many states. Some states, such as Wisconsin, do not enforce closed hunting seasons for wild boars, and actually allow citizens to shoot the animals without a hunting license.
Some states are resorting to more creative tactics. Alabama has been researching oral contraceptives that work on the boars but not other wild animals. The idea is to put the contraceptives in bait for the pigs to eat, thereby slowing population growth.
It's also illegal to own or sell wild boars in many states, including in Michigan, Missouri, Kentucky, and New York.
Cane toad
Here's a species that doesn't cause much trouble for the US, but is a big concern for our Aussie neighbors.
The cane toad was originally supposed to be a force for good, not evil. Native to Central and South America, it was brought to Australia in the mid-1930s in the hopes that it would gobble up cane beetles, which were attacking sugarcane plantations on the continent. Instead, the toads ran amok, reproducing into the millions and becoming a major nuisance on the island.
Cane toads are toxic, so one detrimental side effect is that they tend to poison native animals, like birds or snakes, who eat them. The toad is also thought to compete with native species for resources, particularly nesting space, according to the Australia Department of the Environment.
As one method of control, the Department recommends scooping cane toad eggs out of water sources and discarding them. And more cutting-edge control methods may be on the horizon as well. An Australian news source reported in February that researchers from the University of Sydney were studying a technique that involved luring cane toad tadpoles into traps. This can be done by lacing the traps with cane toad poison, which the tadpoles are apparently attracted to.
But others are taking more extreme measures. Some companies actually sell cane toad leather — that's right, leather made out of the cane toad's skin. Various companies will sell you cane toad leather handbags, belts, and even shoes.
Lionfish
The mighty lion may be king of the jungle, but the lionfish is threatening to become king of the sea. Native to the Indo-Pacific and the Red Sea, this flashy fish first showed up off the coast of Florida in 1985, according to the Florida Fish and Wildlife Conservation Commission. Nobody is completely sure how it got there, but it looks like it intends to stay.
Since then, the lionfish has crept up the East Coast and around the Gulf Coast of the US and is also showing up off the Atlantic coast of South America. It's one nasty customer, preying on smaller native fish (and also competing with bigger native fish for the food source). In addition, those fancy spines are actually full of venom, and they have no known natural predators.
Ecologists worry that the lionfish could have serious negative impacts on local fish populations and coral reef ecosystems. Florida Fish and Wildlife encourages people to remove lionfish from the water if they see them.
And other organizations are taking things a step further: the National Oceanic and Atmospheric Administration (NOAA) actually encourages people to eat lionfish. While their spines are venomous, their flesh is perfectly safe and — according to NOAA — quite tasty.
Asian tiger mosquito
This nasty insect also has an unusual origin story: It's believed to have arrived from Asia in a shipment of old tires, sent to the states for recycling. Now that it's here, it's not only a major nuisance — it's also a potential public health concern.
The Asian tiger mosquito, easily recognizable with its black-and-white striped body, is an aggressive biter, according to the Center for Invasive Species Research at the University of California, Riverside. And it can serve as a vector for a range of unsavory diseases, including West Nile virus, dengue fever, encephalitis, and particularly chikungunya.
It's already spread to 26 states in the US, and scientists worry that rising temperatures associated with climate change could allow it to push its range even further north in the future.
Controlling the mosquito presents a challenge. Most communities recommend that citizens do their best to eliminate mosquito breeding habitats by getting rid of any stagnant water on their properties. But some researchers are looking into more creative methods. There's been some preliminary research into genetically modifying the Asian tiger mosquito to produce flightless females who would be unable to breed, thus reducing the mosquito population.
The biotech company Oxitech has already succeeded in producing a genetically modified version of the "yellow fever mosquito," the other mosquito commonly found throughout the US — but controversy over the safety of genetically modified organisms has prevented the company from releasing the insects in the country yet. Whether the Asian tiger mosquito will meet with the same challenges remains to be seen.
Asian carp
Okay, so the Asian carp isn't just one species. It's actually a name that's applied to a handful of Eurasian carp species which now exist in the US as well. These include the black carp, silver carp, bighead carp, grass carp, and common carp.
These fish made their way into American waters in a few different ways, according to the US Fish and Wildlife Service. Some escaped from research facilities, some were stocked illegally by individuals, and some were even stocked by federal or state agencies to eat up the algae in ponds used for aquaculture.
These carp are now becoming a serious problem in the Mississippi River basin, where they outcompete other fish for plankton, vegetation, and other food sources. And the black carp actually eats snails and mussels, meaning it could pose a direct threat to invertebrate populations in the US. Additionally, silver carp have a nasty habit of leaping into the air when startled, sometimes landing on boats or the people riding in them and potentially causing damage or injury.
Authorities are concerned that the fish, which has been found as far north as Minnesota, may soon establish itself in the Great Lakes, where it would likely spread quickly and wreak havoc on local fish populations. To that end, experts on working on ways to stop the fish from spreading. The Mississippi National Parks Service reports that some agencies are working on developing effective barriers to keep the fish from swimming further upstream.
Reducing the population that already exists is a trickier problem. Fishing is one obvious technique. And turning the carp into food is a good incentive to fish them. Carp isn't the most popular dish in the US, but it's common cuisine in China and other parts of Asia. So far, there hasn't been much interest in exporting the fish abroad. But Moon River Foods in Mississippi, a subsidiary of a Chinese company, has plans to catch, fillet, and package the fish for commercial sale. And at least one Illinois company is experimenting with turning the carp into fish oil and animal feed.
Brown tree snake
The brown tree snake is probably another case of accidental importation — not in the US, but in Guam. Native to Australia, Indonesia, and Papua New Guinea, the brown tree snake was likely brought over to Guam in cargo some time in the 1950s. Once there, it wasted no time in causing mayhem among local wildlife populations.
The snake, which eats small animals such as birds and lizards, has caused widespread declines among native wildlife species, including the extinction of several bird species on the island. It's also responsible for frequent power outages, thanks to its habit of slithering onto electrical wires.
The government has launched some imaginative attacks in response. It turns out acetaminophen — a drug commonly used as a pain reliever and fever reducer for humans — is highly toxic to the brown tree snake. So in 2010, federal agencies began implanting acetaminophen tablets into dead mice and dropping them into Guam's forests from helicopters. The mice are outfitted with little parachutes, which are designed to snag in tree branches, leaving the mice dangling enticingly for the snakes to find.
Invasive species may be taking over certain parts of the world, but from genetic engineering to mouse parachutes, at least we're fighting to save our ecosystems with creativity and style.
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