Anyone who has ever watched an episode of Animal Planet knows that ecosystems are fragile, relying on the delicate balance of species and resources. But what is less-known is the high economic cost when that balance is upset by animals that are alien to an area.
Some animals and insects -- including killer bees, Asian carp and Asian mongooses -- are introduced by humans to correct an imbalance, but end up posing an unforeseen threat to other species. In some cases, species that were once endangered grow out of control due to the efforts of concerned scientists and environmentalists to protect them. Caught between the danger of doing too much or too little, only one thing is certain: when it comes to the environment, each option carries a high price.
Here are 10 animals that, for one reason or another, have overpopulated their environment, threatening other species, resources and, ultimately, themselves.
It's hard to believe, but a little over 100 years ago, over-hunting drove Canada geese close to extinction. New York State officials decided that the birds needed help if they were to survive and, from 1958 to 1963, wildlife experts released scores of geese into the state's forests. Before long huge flocks were settling throughout the state.
Today, officials face the opposite problem: There are more than 200,000 geese in New York, and they have begun endangering public health by soiling parks and lakes, stripping farmers' fields and getting in the way of airplanes. According to one report, over the last ten years, they have struck 78 planes in the area, costing $2.2 million in aircraft damage and killing at least 24. In fact, 2009's "Miracle on the Hudson" plane crash was caused by Canada geese.
In the last six years, the government has tried to cut down the population by tripling the bag limit for hunters and gassing an estimated 14,000 birds. In New York, Mayor Bloomberg's July 2010 decision to euthanize 400 geese -- dubbed "the Goosicide" by opponents -- led to widespread protests as angry bird-lovers picketed city hall with signs reading "Give Geese a Chance."
Looking like a cross between an experimental aircraft and a tub toy, the cownose ray isn't something that most people want staring back at them from a dinner plate. But Virginia officials are trying to convince the public that the graceful animals, rebranded as "Chesapeake Rays," are a delicious substitute for veal. This strategy is aimed at trying to protect the Chesapeake Bay's oyster industry, a once-thriving business that has fallen on hard times. Currently valued at approximately $4 million annually, improved aquaculture and the lingering effects of the BP oil spill on the Gulf of Mexico oyster industry could position the Chesapeake industry for a ten-fold expansion in the next few years.
Unfortunately, getting there will mean dealing with the rays. The huge ray population -- which has expanded because of the overfishing of coastal sharks -- keeps gobbling up the thousands of farmed oysters that wildlife officials have farmed throughout the Bay. So here's a quick recap: too few sharks = too many rays = too few oysters = stingray fricasee. Bon appetit!
In the Great Lakes, fishing is big business: a $7.5 billion industry, it supports an estimated 800,000 jobs. Unfortunately, the lakes -- the world's largest freshwater ecosystem -- are extremely fragile, and are under attack by a number of invasive species. Already harassed by zebra mussels and sea lampreys, fishermen in the area are frightened by another potential threat: Asian carp. Imported by catfish farmers in the 1970's to skim algae from aquaculture ponds, the fish escaped from their original home and migrated throughout the Mississippi River, massively depleting plankton and pushing out other species.
In 2004, a coalition of government agencies, spearheaded by the Environmental Protection Agency, built a $9.1 million electric barrier to keep the invasive fish out of the Great Lakes. So far, the barrier -- and a subsequent $3 million fish kill -- have kept the lakes carp-free, but in 2010, a 19-pound specimen was caught in Lake Calumet, less than six miles from Lake Michigan.
Unlike most invasive species, coyotes are native to North America, with a natural habitat that extends from Alaska to Central America over terrain ranging from mountains to plains to -- these days -- cities (in one notable case, a coyote even staked out a Chicago Quiznos).
But the wily canines are an expensive nuisance: the major predators of cows, sheep and other livestock, they also prey on household pets in many suburban areas. A 2004 survey by the National Agricultural Statistics Service (summarized in this livestock report) found that coyotes were responsible for killing an estimated 135,600 sheep and lambs worth $10.7 million. The extensive cost to agriculture has led government officials to spend millions every year poisoning, trapping and shooting an estimated 90,000 coyotes.
It was bad enough when Floridians just had to worry about Burmese pythons: the Everglades are infested with an estimated 100,000 of the gargantuan snakes, many of which are descended from abandoned pets. Recently, however, African rock pythons -- an even larger, more aggressive python species -- have been found in the swamp, and experts worry that the new snakes might be interbreeding with the Burmese pythons, yielding what some officials have referred to as a "super snake." Thus far, the pythons have largely stayed in the Florida swamps, but experts warn that the new hybrid could be very adaptable, potentially spreading as far north as Virginia and all the way to California. Along the way, the snakes -- which are capable of eating goats and crocodiles -- could eventually pose a major threat to children, pets and livestock.
While their proper name is "Africanized honey bees," the name "killer bees" caught the country's attention in the late 1970's, when thousands of hybrid African/European bees began working their way North from their home in Brazil. In 1978, Irwin Allen -- producer of disaster films The Poseidon Adventure and The Towering Inferno -- capitalized on the widespread terror, releasing The Swarm, a shlocky enviro-horror flick that predicted what would happen if a killer bee swarm arrived in the U.S.
In truth, Africanized honey bees are not as horrifying as The Swarm indicates. While they are more aggressive about defending their nests, their stings only kill an estimated one to two people per year. On the bright side, they also produce far more honey than most bees, a factor that has encouraged many beekeepers to interbreed the Africanized bees with their existing stocks.
In 1890, drug manufacturer Eugene Scheiffelin had a beautiful, romantic idea: he decided to use his money to bring all the birds mentioned in Shakespeare's works to New York City. While his experiments with thrushes and skylarks failed, the 100 starlings that he imported from Europe thrived in their new home. By 1942, their descendants had spread across the country.
Today, an estimated 200 million starlings are flying around North America. The birds gather in massive flocks that force out native species, denude acres of crops, and disrupt airports. According to a study by Cornell University, the birds cause $800 million in agricultural damage each year, and federal aviation officials say that they have caused millions of dollars in damage to the airline industry. Little wonder, then, that the U.S. Government has declared war on the pests, poisoning over 1.7 million in 2008.
Mountain Pine Beetles
Most invasive pests simply overrun an area, eating everything in their way, but mountain pine beetles are especially sneaky. Pine trees fight invaders by increasing their flow of sap, a defense that forces most bugs out of the tree. To fight against this, pine beetles carry "blue stain," a fungus that disables the tree's usual defenses. Soon, the pine tree withers and dries up, unable to absorb water.
The current pine beetle infestation, which began in the mid-1990's, may be the largest forest insect blight in North American history. As of this year, the beetles have destroyed an estimated 3.6 million acres of trees in Colorado and Wyoming. It is difficult to estimate the full cost of this infestation: in the short term, the U.S. Forest Service committed $40 million for cleanup efforts in 2009. However, the long-term impact of the infestation is almost immeasurable: in British Columbia, where the tiny bugs destroyed a forest area roughly the size of California and New York combined, they will end up costing an estimated 11,000 jobs over the next 14 years.
Brown Tree Snakes
Island ecosystems are particularly vulnerable, a fact that was driven home in the 1950's when brown tree snakes hitched a ride to Guam aboard U.S. military transport planes. The island, which had no native snakes and few natural predators, was quickly overrun as the highly venomous vipers decimated native animal species, including the once-abundant Micronesian kingfisher which no longer exist in the wild on the island. Despite efforts to control the pests with poison, Guam currently has an estimated 13,000 brown tree snakes per square mile. While officials have mounted vigilant attempts at containment, some of the hitchhiking snakes have also been sighted on Hawaii, where worried officials have instituted an aggressive control program.
If brown tree snakes ever get a toehold on Hawaii, they will find a tough reception. One famed snake predator, the small Asian mongoose (also known as the Indian mongoose), already infests the islands. In the 1800's, a sugar cane planter in Hawaii brought 72 of the little animals to help control an overwhelming rat population. Established on all the islands except Kaua'i -- according to legend, the animals bit a dock worker, who responded by hurling their cages into the ocean -- the mongooses ate a few rats, but soon developed a taste for easier prey, including the hundreds of endangered species that can only be found on the islands. Today, they are barely kept in check through extensive trapping and poisoning.
The mongooses' cost to the islands are measured less in dollars than in the richness and diversity of Hawaii's animal populations: many of the islands' water birds have been driven to the brink of extinction by the furry little hunters. Enthusiastic consumers of eggs and baby birds, mongooses have a particular preference for the Hawaii's state bird, the Nene or Hawaiian goose. Reduced to a mere 30 birds in 1952, conservation efforts have helped the geese to rebound: today, there are an estimated 1,300, at least half of whom are clustered on Kaua'i.