Buzz
The natural world teems with creatures that pose threats, prey on others, or rule entire ecosystems. Yet in this unsettling narrative, we delve into the worst offenders of nature's rebellion. While order does exist in nature amid the violence and turmoil, the careless introduction of foreign species by humans can easily disrupt this balance. Without natural predators or boundaries, these mass invasions often wreak havoc on species, ecosystems, and even human settlements unprepared for the onslaught.
10. Crown-of-Thorns Starfish
The crown-of-thorns starfish is a menacing sight, resembling a creature from another world. Growing over 33 centimeters (13 inches) in diameter and equipped with up to 21 sharp, defensive arms, this starfish is protected from most predators as it feasts on coral polyps. Unlike many introduced invaders, the crown-of-thorns has become problematic even within its native habitat, primarily due to environmental disturbances. With its insatiable hunger and rapid reproduction, each starfish in a group can devour up to six square meters (64 square feet) of coral reefs annually, decimating vast areas of reef. Experts believe that the outbreaks are linked to human-induced shifts in the ocean ecosystem, particularly increased nutrient pollution. As a result, some regions have initiated population control programs, injecting the starfish with deadly toxins to curb their spread.
9. European Starling
The European starling was brought to North America by Eugene Schieffelin, an American who was deeply fond of Shakespeare. Schieffelin had a personal mission to introduce every bird mentioned in Shakespeare's works to the continent. He released 60 starlings in Central Park, and from that point, the birds spread across North America, reaching as far as Alaska and Central America. These birds took over urban spaces, ravaged crops, and caused significant declines and local extinctions of native songbirds, including woodpeckers, bluebirds, and swallows. Their massive flocks pose a hazard to aviation, with 62 people dying in a tragic incident when starlings were sucked into the engine of an American airliner. Despite extensive control measures, the European starling population has reached approximately 150 million in North America.
8. Giant Canada Goose
Although Canada does not have an official national bird, most wildlife enthusiasts would likely consider the Canada goose as the country's most iconic avian species. However, Canada’s vastness allows for various subspecies of Canada goose, each with distinct lifestyles. In a case of domestic rather than foreign invasion, resident Canada goose subspecies from Canada's interior are damaging estuaries along the Georgia Basin, a critical stopover for thousands of migratory birds and a vital salmon habitat that, in turn, supports human populations and endangered orca whales.
Former federal wildlife expert Neil K. Dawe has conducted field research across several estuaries, publishing findings that suggest the geese are wreaking havoc on the habitat and causing the collapse of the local food chain.
7. Burmese Python
While many invasive species are relatively small, the Burmese python stands out as a massive and potentially lethal giant. Originally introduced to the Florida Everglades, these colossal constrictors are among the largest snakes on earth, reaching lengths of over five meters (16 feet) and weighing up to 90 kilograms (200 pounds). The pythons, believed to number in the thousands in this habitat far from their native southern Asia, possess powerful, razor-sharp teeth in their jaws. These giant snakes are threatening to decimate the wetlands, preying on native species, even taking on the usually indestructible American alligator. The snakes have been designated a priority for removal by state wildlife management authorities, but control measures have largely failed so far.
6. Cane Toad
The cane toad serves as a cautionary tale of how introducing one species to control another can backfire spectacularly. Native to Central and South America, this massive and toxic amphibian (weighing up to 2 kilograms (4.5 lbs) and measuring as much as 23 centimeters (9 inches) long) was released in the early 1900s to curb sugar cane beetles on tropical island plantations. Instead of solving the problem, the toads proliferated across a wide array of habitats, pushing native wildlife into decline. Among the affected species are predatory lizards, marsupial mammals, and songbirds. Even the formidable saltwater crocodile, known for its man-eating tendencies, faces the threat of its nests being raided by cane toads.
Like many invasive species, the cane toad population remains unnaturally high in its new environment due to the lack of natural predators that can feed on them or withstand their toxic defenses. Proposals to use a virus to control the toads raised concerns that such an approach might trigger further ecological imbalance by harming native species. In an ironic twist, the toad's own toxin is now being used to attract and eliminate their tadpoles.
5. Brown Tree Snake
When a predator is introduced to an isolated island, native species, unprepared to resist such a threat, are often overwhelmed, and a lack of natural predators causes a population explosion (an effect intensified by the limited space). When the brown tree snake reached the island of Guam after World War II, likely stowing away in a cargo hold, it triggered what might be the most catastrophic ecological disaster ever caused by an introduced species. These mildly venomous snakes proceeded to eradicate most of the native forest-dwelling vertebrates and caused severe disruption, including painful bites and power outages when they invaded human settlements. Efforts to control the snakes have involved dropping dead mice laced with poison, as the reptiles have grown to lengths of up to three meters (10 feet) due to the abundant, unnatural food supply.
4. Oceanic Rat And Mouse Plague
Ships don’t just carry humans, but also some of humanity’s most destructive pests: the Norway rat and the house mouse. These invasive rodents, often spreading diseases, bring devastation to island ecosystems, wiping out entire seabird populations when they reach port. The rats devour eggs, young, and even adult birds such as petrels, auklets, and other waterfowl that rely on nesting sites free from land-based predators. The global crisis of seabird extinction has been exacerbated by the presence of these invasive rats, with predation rates soaring to catastrophic levels, including up to 25,000 chicks per year for the endangered Henderson petrel. Equally perilous are the house mice, which threaten species like the critically endangered Tristan albatross and even consume chicks alive.
3. Brown-Headed Cowbird Invasion
Invasions by land animals can occur when human-induced changes to land use provide new opportunities for species to prey on others or, as with the brown-headed cowbird, parasitize other birds' nests. Originally, brown-headed cowbirds evolved on the North American plains, where they followed buffalo herds to feast on disturbed insects. The buffalo’s movements prevented the birds from building their own nests and raising their young, so they adapted by laying their eggs in the nests of other birds. Over time, many bird species developed ways of removing or failing to incubate these foreign eggs.
However, as forests fragmented into smaller patches, cowbirds spread over vast areas of woodland, contributing to the decline of forest-dwelling songbirds that weren’t equipped to deal with the parasitic eggs, leading to the starvation of their own offspring. To counter this invasive “native” species, conservationists sometimes resort to culling cowbirds in efforts to protect songbirds. The cowbird invasion even led to the rare Kirtland’s warbler being pushed to the brink of extinction.
Email Alexandre for nature writing services and tours in Canada.
2. Crab-Eating Macaque Monkey
While humans are often cited as the primary invasive species on Earth, it’s rare to consider monkeys as part of this problem. However, the crab-eating macaque made it onto the International Union for Conservation of Nature’s list of the 100 Worst Invasive Species. These adaptable primates, originally from Southeast Asia, have successfully infiltrated various island habitats after being introduced by humans.
Like many land invaders, the clever macaques pose a threat to vital tropical bird breeding areas and are believed by some to have played a role in driving endangered bird species toward extinction. Additionally, macaques can display aggression towards humans and carry an endemic strain of herpes virus that can be fatal to humans. The virus presents similar symptoms to herpes simplex but can lead to severe brain damage and death if not treated properly.
1. Worldwide Feral Cat Invasion
While cats are often considered man's second-best friend, they can also be a major invasive threat, wreaking havoc on native wildlife in unfamiliar environments. With both direct and indirect help from humans, feral cats have contributed to the deaths of millions of songbirds that are not equipped to fend off these silent hunters. The damage to island birds has been especially severe. In one rare case, a single cat is thought to have driven the Stephens Island Wren, a New Zealand bird, to extinction. Many islands and continents have witnessed drastic declines in seabird populations and native mammals due to feral cat invasions. Despite this, some researchers argue that cats may play a beneficial role by controlling smaller predators like rats, potentially saving certain species from further harm.
