Introduction of non-native species to a new environment is often done completely by accident. Anywhere people travel, something unseen can be traveling along, too. Planes, ships, and other methods of distant travel have taken critters to places they don't belong, and we only discover the problems they cause much later.
1. Snakes on Guam
Sometime between 1945 and 1952, the brown tree snake (Boiga irregularis) was introduced to the island of Guam, where it had never lived before. There may have been several instances of snakes stowing away on cargo ships, as Guam is a major transit point. Snakes flourished on Guam, where there was plenty of food available in the form of birds, bats, and lizards. By 1990, almost all the native birds were gone, and plans were developed to battle the snakes with multiple weapons: poison, fumigation, barriers, trapping, habitat modification, and port detection with dogs. But the snake damage continued. Since they had eaten all the birds and most of the fruit bats, pollination of native plants and trees suffered. In 2010, a new plan began: a government conservation team stuffed the carcasses of dead mice with Tylenol and airlifted them over the forests of Guam. A brown tree snake is one of the few snake species that will eat an animal it hasn't killed, and a small dose of acetaminophen is deadly to them. The "mice bombs" were attached to pieces of cardboard and paper streamers, so they would be caught in tree limbs where the snakes reside. The effectiveness of this plan has not yet been publicized, but scientists don't expect it to wipe out the snakes; they just hope to control their numbers. Photograph by Flicker user Armed Forces Pest Management Board.
2. Kudzu Bugs
Kudzu is an invasive vine that was imported from Japan in the 19th century as cattle feed, to use for erosion control, and as an ornamental plant. It is native to China, where the environment controls its spread. However, in the U.S. it flourished wildly and now covers the South. In 2009, an Asian insect called Megacopta cribraria reached the U.S., possibly by plane, and thrived by eating kudzu. You would think that a biological control of the weed would be welcomed, but there are other consequences to consider. The kudzu bug spread through several southern states, and is eating soybeans and bean crops as well as kudzu, which gave the bugs the name Bean Plataspid. They also invade homes and smell really bad, which is why they are also called Globular Stink bugs. Photograph by Flickr user Charles Lam.
3. The Catalina Island Bison
Santa Catalina Island is a few miles off the coast of Los Angeles. In 1924, a film crew shot a Zane Grey movie there called The Vanishing American, and brought 14 head of bison with them. The animals never showed up in the finished film, however. The story goes that the film crew left the bison behind after filming in order to save the money it would cost to transport them. By 1969, there were 400 bison on Catalina Island, and they were eating up the native plants. The Catalina Island Conservancy has employed various methods to control the size of the herd. A number of bison have been shipped out over the years: at first they were sold, then many were relocated to the Great Plains in multiple shipments. In the past few years, the Conservancy has turned to birth control methods, which appear to work and are much cheaper and less stressful than relocating the large animals. The Conservancy is also working to save the Catalina Island fox, which is a native species, and control invasive plants. Photograph by Flickr user Kenneth Hagemeyer.
4. Mussels in Michigan
Zebra mussels and Quagga mussels are both invasive species which arrived in the Great Lakes by attaching themselves to ships. Zebra mussels are native to the Caspian Sea and were first spotted near Detroit in 1988. You can follow the spread of Zebra mussels by running your mouse over the dates on this map. The Quagga mussel is native to the Dneiper River area of Ukraine, but has also invaded the Great Lakes and other areas of the U.S. Both species are upsetting the Great Lakes ecosystem:
These mussels have permanently changed the ecosystem. Before the mussels invaded, Lake Michigan water was mostly cloudy and millions of tiny microorganisms provided a food base for fish. Because the mussels filter the microorganisms, the waters today are surprisingly clear, allowing light to penetrate to greater depths, which in turn promotes prolific, nuisance algae blooms.
The mussels are also thought to be one of the main reasons that the population of the crustacean Diporeia, a major food source for fish, is declining rapidly, although industrial pollutants may also be a factor. Zebra mussel shells photographed by Flickr user Benny Mazur.
5. Farmed Algae Eaten by Shrimp
In order to curb global warming, there have been several projects to dump iron dust into the sea in order to encourage algae growth, because plankton absorbs carbon dioxide (CO2), a greenhouse gas. However, the location of these dumps makes a big difference. In 2009, ten tons of ferrous sulphate were pumped into the waters off Argentina. The algae bloomed, alright, but it was not the species that was expected. The project hoped to encourage growth of large diatom algae, but instead, tiny haptophytes gobbled up the iron. Haptophytes are the preferred prey of copepods, which are small shrimp-like animals. In this instance, the experiment was a failure and the iron was a loss, but scientists think that that the explosion of copepods will do no harm to the environment. They think. Copepod photograph by Flickr user Labut.