Island ecosystems are easily unbalanced by the introduction, accidental or otherwise, of invasive species. The results can range from mildly amusing to full-fledged ecological disasters. These 7 amazing islands overrun by animals provide us with a wealth of environmental test cases offering valuable lessons for the human stewards of our rapidly shrinking Island Earth.
1. Cats - Tashirojima, Japan
Images via: Tsunami Animals and TravelingGuide.net
Only about 100 people live on Tashirojima, a small island in the Pacific Ocean just off the coast of northeastern Japan. They’re outnumbered by semi-feral cats whose omnipresence has brought the island fame and the colloquial name of “Cat Island”.
Images via: Prafulla.net
The cats are not native to Tashirojima, having originally been brought to the island centuries ago to control mice that were damaging a once-thriving silkworm industry. Once established, the cats gained the affection and admiration of fisherman who noted the felines’ uncanny ability to predict storms.
Image via: The Atlantic
Tashirojima suffered severe infrastructural damage from the devastating Great East Japan Earthquake in March of 2011, chiefly from the ensuing tsunami which flooded low-lying areas of the islands. The cats, however, proved their rumoured weather forecasting abilities were no folk tale by moving to higher ground before the tsunami struck.
2. Chickens - Kaua’i, Hawaii
Images via: Eliduke, Polloplayer and Ceder.net
Chickens were first brought to the Hawaiian Islands by the first waves of Polynesian colonists over 2,000 years ago. The chickens were kept and bred mainly for their meat and eggs though roosters were selected for cock-fighting. In the modern era, chickens of American and European ancestry were imported to the island.
Images via: Cloudy and Cool and SFGate
Both birds and islanders lived in relative harmony until 1992, when Hurricane Iniki struck the Hawaiian Islands. The storm hit Kaua’i at its peak intensity and scattered cooped chickens across the island.
Image via: Suburban Misfit
The freed chickens rapidly reverted to feral ways and the wild population exploded. Capturing the chickens for food isn’t a workable option as the current mix of Polynesian and European stock combined with the chickens’ non-grain food results in gamey, off-flavoured meat. Aside from cluttering roads, beaches and golf courses, however, the chickens don’t appear to be causing any noticeable environmental damage.
3. Rats - Montecristo Island, Italy
Images via: The Independent and Daily Mail UK
The island of Montecristo, made famous by the 1844 novel The Count Of Monte Cristo by French writer Alexandre Dumas, is situated in the Tyrrhenian Sea east of Corsica and off the western coast of Tuscany, Italy. The island’s ruggedness has helped it to shrug off repeated attempts to colonize it since the end of the Ice Age - humans have failed but black rats have been overwhelmingly successful.
Image via: In Your Tuscany
With an estimated saturation of one rat per square yard on an island just 4 square miles in area, an estimated 12 million rats call the island home…and call its native wildlife “dinner”. In a belated effort to save the island’s shrinking resident seabird colonies from the voracious rodents, the Italian government is planning to airdrop 26 tons of poisoned pellets which will hopefully eradicate the rats.
4. Spiders - Guam
A walk through the jungles of Guam has never been a very pleasant proposition but lately it’s downright horrific. Vast sheets of silky webbing fill the spaces between trees and as anyone knows, where there are webs, there be spiders…about forty times the expected amount at that!
Image via: Futurity
Guam’s spider population explosion can be easily explained though remedying it is a much tougher nut to crack. In the 1940s, brown tree snakes landed on the western Pacific island (probably by hitchhiking on cargo ships) and found a paradise where they had plenty of food and very few predators.
Images via: Govteen, Rice University and FrenchTribune
As the years passed, native bird populations plummeted and the spiders normally kept in check by the birds boomed. Removing the snakes would help restore Guam’s ecological balance but that may just create more problems. In the meantime, if you don’t like spiders and snakes, stay the heck away from Guam!
5. Rabbits - Okunoshima, Japan
Another Japanese island, another island overrun by critters! This time it’s Okunoshima, a small island in the Inland Sea whose main feature is a 740ft tall hydroelectric pylon. Okunoshima harbours a darker side as well: it hosted the country’s main poison gas production facility from the late 1920s.
Images via: MNN, Mestarhanta and Fanpop
After World War II ended, American occupation forces disabled the gas factories and disposed of any stored poison gas. The island was redeveloped as a park and in 1971 rabbits were released to roam freely, while a Poison Gas Museum was established in 1988 to educate visitors about the once-secret poison gas program.
Image via: Tumblr/Creepingoat
Word of Okunoshima’s friendly and abundant population of rabbits has spread and these days the island is the focus of rabbit-based tourism. The rabbits themselves do not appear to be adversely affecting the island’s plant and animal life, and unlike other places where rabbits have been introduced, Okunoshima’s rabbits are protected from hunting.
6. Mice - Gough Island
Images via: Evolutionm Forums and SANAP
Gough Island is about as far away from dry land as one can get. This South Atlantic speck measures just 13 km (8.1 mi) by 7 km (4.3 mi) and sits roughly 2,700 km (1,700 mi) from South Africa’s Cape of Good Hope. Isolated as it is, Gough Island has a long history of human visitation going back to the year 1505 and during one of those visits, common house mice escaped from one of the landing ships. The humans didn’t stay but the mice did.
Image via: ACAP
Unchecked by predators and unhindered by seabird chicks that, while massively outweighing them, had no way to defend themselves, Gough Island’s mice ran amok…and as time passed, their average size increased as well. Attacking chicks in their burrows during the night, gangs of mice make short work of many threatened species and in total their population has ballooned to more than 700,000. Rodents of unusual size and numbers!
7. Crabs - Christmas Island
Images via: NowPublic, Arkive and The Australian Empire
It’s beginning to look a lot like Christmas - at least, the island by that name annually gets a huge splash of red to go along with its greenery, and it usually happens in November. The scarlet splash comes by virtue of the Red Crab, native to Christmas Island and numbering in the tens of millions. Compare that to the human population of only 1,500 or so, and you’ve got the makings of an annual overrunning with a capital O!
Image via: Amusing Planet
Not only do the Red Crabs migrate from their inland rainforest burrows to the sea, their offspring perform the feat in reverse creating difficulties for pedestrians, drivers and trains (until the railway was closed in 1987).
Images via: National Geographic and SaveVid
Curiously, there is no notable mention of the crabs in chronicles left by early colonists. It’s possible the extinction of two types of native rat in the early 20th century may have allowed the Christmas Island crab population to explode. Nature finds a way, as always: invasive yellow “crazy ants” from Africa are blamed for a sharp reduction in crab numbers noted in recent years.
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