Attack of the Alien Invaders, National Geographic Magazine

In our increasingly connected world, global trade and travel are accelerating the movement of organisms to places that they couldn’t have reached without our help. It is a thoughtless rearrangement of misplaced creatures, or as one biologist put it, “evolution on steroids.”

Biological invasions rank second to habitat loss as a threat to native biodiversity. Most people are unaware of the enormous problem, partly because the invaders are so common, and partly because few understand that our pests, weeds, and diseases are related.

The extinction rate is accelerating rapidly. Over the next 100 years, it is estimated that roughly half of the species on Earth will completely or functionally disappear. Forty percent of those extinctions are caused by invasions. And we are making the planet increasingly hospitable for the weedy species—things that thrive in disturbed, human-dominated environments.

One example in the plant world is Kudzu, which drapes over tree canopies in the South. First introduced from Asia in the 1800s as a crop, it was heavily planted in the ‘50s along roadsides for erosion control. Anything that doesn’t move may be covered since it grows a foot a day.

Other invasives are so commonplace that they are not recognized as a problem species—like a litter of unwanted kittens. The kind-hearted may volunteer to feed homeless cats that roam a neighborhood, but there are an estimated 60 million feral cats in the U.S., and they are responsible for the deaths of over a billion small mammals and hundreds of millions of songbirds.

There are 10,000 feral cats in the Florida Keys alone. Once a month volunteers in Islamorada trap feral cats, and a vet comes to spay and neuter them to try to reduce the forever-growing cat population.

Some very unlikely exotic species have become invasives, and the pet industry is largely responsible. There are few controls on imports — 22 of 24 species of pythons are available at pet stores, along with boas, crocodiles, iguanas, and bird-eating spiders.

And although many appropriate pets are available that capture the attention and curiosity of a young child, there are no warning labels on reptiles and other species that can quickly grow into unmanageable or dangerous animals.

A young, one-foot-long Burmese python will grow to six feet in length the first year and ten the following year. It can grow to a total of 20 feet and 200 pounds and can live more than 25 years. It’s no wonder they are dropped off in the wilds of Florida swamps.

An eight-foot-long Burmese python is one of the smaller snakes caught along the main road into Everglades National Park. Wildlife biologists there say a breeding population from released snake that is established, and they fear their numbers will explode.

An island Ecosystem such as Hawaii is especially fragile and over the years is highly impacted by invasive plants and animals. A family that farmed taro for seven generations now watches as the golden apple snail decimates their crop.

The story of the apple snail’s origin seems as innocent as that of many introduced species. To supplement a family’s meager farming income, the apple snail was introduced, hoping it could be cultivated as escargot.

Not only was it a bust as a cash crop, it became an invasive species by growing in numbers beyond control and ruining taro and rice crops.

The newest arrival to Hawaii is the Coqui, a frog that has moved from island to island with its chirpy little call that has the decibel level of a lawn mower. War is waged on this frog because its numbers are exploding and it has no predators. Lawsuits now force homeowners to disclose the fact that they have these frogs because Hawaiians are so upset by the noise. It was first imported on plant material and even carefully quarantining goods have only slowed its spread.

Another invasive in Hawaii is the Axis deer, originally a royal gift to the islands in 1868 from Hong Kong. Five were brought to Maui in 1959 for hunting and now there are 10,000 deer eating their way through Hawaii’s native plants. Opinions are sharply divided on managing axis deer.

A fence was built around endangered plants on Haleakala National Park to protect them from the deer, and the deer are hunted, in an effort to eradicate them within the fenced area.

But people also come to Hawaii to hunt Axis deer. It is a good source of income for people on the island of Lanai who are guides for those who enjoy the sport of hunting the small, elusive deer that never loses its spots.

Besides the disturbing environmental imbalance that invasive species bring, there is a huge economic cost. Biological invasions in the U.S. alone cost $137 billion annually, which translates to about $2,500 a year for every American family.

The crackdown on invasive species is not a war to win. Invasions are chronic, and require expensive, unglamorous, sustained solutions.