1The Hippos of Colombia
Escobar imported a whole menagerie of animals into his ranch, Hacienda Napoles. After authorities had seized the property in the early 1990s, most of the animals were sent off to zoos around the country, but four hippos remained. The lake at Hacienda Napoles was an ideal habitat for the hippos and, two decades later, there are over fifty! However, some are not content to live on the ranch any longer—the slow-flowing river waters have made the entire area a haven for hippos. The free-roaming beasts are now a danger to townspeople, who refuse to let any harm come to their beloved, but out-of-place mascots. (Source 1 | Source 2 | Photo)
2The Pythons of Florida
They were first seen in Everglades National Park in the 1980s, but experts didn't realize the snakes were reproducing until 2000. Today, the number of pythons seen in the park has increased dramatically (estimates say there are anywhere from 30,000 to 300,000 in southern Florida alone) and the population seems to be expanding northwest.
While the snakes are relatively docile and don't pose a serious threat to humans, they do threaten native wildlife in the area and have already drastically affected the populations of raccoons, opossums, bobcats, rabbits, foxes and other mammals.
It is now illegal to import Burmese pythons into the U.S, and for the existing wild population to be reduced, significant action needs to be taken. Unfortunately, all current control methods have proven unsuccessful in the Florida Everglades. (Source 1 | Source 2 | Photo)
They've even grown larger and are living longer than their rural counterparts.
How well have they adjusted? In some instances, they've even learned to observe traffic patterns so they can cross the road more safely. Researchers believe their adaptability and natural distrust of people is precisely what makes them such successful city-dwellers.
Surprisingly, the coyotes are improving the areas where they live by helping to eradicate rodents and other unwanted pests—just be sure not to leave your pets outside unaccompanied. (Source 1 | Source 2 | Source 3 | Photo)
4The Squirrels of City Parks
Gray squirrels also became popular with fashionable estate owners in England. Unfortunately, they are now considered an invasive species in the UK and are decimating the population of native red squirrels which are smaller and more prone to disease than their American cousins. In fact, environmentalists in the UK are telling the public that the only way the country's beloved red squirrel can survive is if Brits and Scots actively start killing gray squirrels. (Source 1 | Source 2 | Photo)
5The Rabbits That Overtook an Island
6The Cats of "Cat Island"
The island has traditionally been a fishing village, so cats were imported to protect the catch from mice and rats. While the cat population continued to increase over the next few centuries, it shot up when the island's population started to decline after WWII. Nowadays, the cats outnumber humans on the island, 6:1.
In Japan, cats are considered good luck, so people take care of the cats and often feed them by hand. The cats, like the rabbits of Okunoshima, are extremely friendly, making the island a popular tourist destination for cat-lovers around the globe. The place is so beloved internationally that when residents had a hard time getting food for the animals, they asked the internet and were immediately flooded with more food than they could handle.
It's worth noting that while Aoshima is the most famous "cat island," there are as many as ten other islands in Japan that are overrun by felines. (Source 1 | Source 2 | Source 3 | Source 4 | Photo)
7The Starlings of America
Starlings are pretty, and eat insects, but destroy millions of dollars worth of crops each year. In fact, in a single day, a cloud of starlings can consume up 20 tons of potatoes. If that's not bad enough, they leave droppings all over the remaining crops that are linked to numerous diseases including histoplasmosis (a fungal lung ailment); toxoplasmosis, and Newcastle disease, which kills poultry. They also put native wildlife at risk, bullying birds such as bluebirds and woodpeckers out of their roosts and territories. So far, no eradication method has proven useful. (Source | Photo)
8The Parrots and Peacocks of Hawaii
While parrots are native to the southern hemisphere, none come from Hawaii. Some species (like the red-masked parakeet) are a pleasant, harmless addition to the environment while others (such as mitered conures) are a threat to the island's crops and native forests. As a result, some of the birds are adored by residents while others are on the government's hit list. Like many feral parrot populations, the birds were introduced to the area when they were released or escaped from someone's home where they were kept as pets.
As for peacocks (technically peafowls when you're talking about both genders), which are native to India, they were first introduced to Hawaii by Frances Sinclair in 1860. The beautiful birds soon became a favorite of Princess Kaiulani, who was even nicknamed "The Peacock Princess." The animals now live on all of the Hawaiian islands, but they are a controversial presence—some try to kill the peacocks while others adore the strange birds and even feed them. (Source 1 | Source 2 | Source 3 | Source 4 | Source 5 | Source 6 | Photo)