“Tobacco, potatoes and turkeys came to Europe from America. In exchange, Europeans brought wheat, measles and horses. But whoever thinks about earthworms? Yet they, too, were brought to America by Europeans, and hardly with fewer consequences than those of other, more famous immigrants.” Johann Grolle, German writer for DER SPIEGEL.
As if climate change and the lust for endangered plants and animals weren’t enough to challenge the world’s wildlife biologists, add to those issues the specter of invasive species and you have a three-dimensional Chinese puzzle to solve. An invasive species can be any kind of living organism—an amphibian (cane toad), plant (kudzu), insect (tent caterpillar), fish (silver carp), fungus (Batrachochytrium dendrobatidis, also known as amphibian fungus or Chytrid, bacteria (Haemophilus influenzae), virus (2019 novel coronavirus) or even an organism’s seeds or eggs—that is not native to an ecosystem and causes harm. Species that grow and reproduce quickly, and spread aggressively, with potential to cause harm, are called “invasive.”
An invasive species does not have to come from another country. Lake trout are native to the Great Lakes, but they are considered to be an invasive species in Yellowstone Lake in Wyoming because they compete with native cutthroat trout for habitat. Invasive species are primarily spread by human activities. People, trafficked animals and plants, and consumer goods travel around the world very quickly, often carrying uninvited species with them. Ships can carry aquatic organisms in their ballast water. Insects can get into wood, shipping palettes, and shipping crates. Some ornamental plants can escape into the wild and become invasive. And some invasive species are pets intentionally or accidentally released; Burmese pythons are devastating native species in the Everglades.
When a new and aggressive species is introduced into an ecosystem, it may not have any natural predators or controls. It can breed and spread quickly, taking over an area. Native wildlife may not have evolved defenses against the invader, or they may not be able to compete with a species that has no predators.
The direct threats of invasive species include preying on native species, outcompeting native species for food or other resources, causing or carrying disease, and preventing native species from reproducing or killing a native species’ young. There are indirect threats of invasive species as well. Invasive species can change the food web in an ecosystem by destroying native food sources and may provide little to no food value for wildlife. Invasive species can also alter the abundance or diversity of species that are important for native wildlife. Aggressive plant species like kudzu can quickly replace a diverse ecosystem with a monoculture of just kudzu. Asian carp, the brown marmorated stink bug, and zebra mussels are prime examples of these capabilities. But there are others. A lethal case of unintended consequences…
The Africanized honeybees in the Western Hemisphere are descended from hives operated by biologist Warwick E. Kerr, who had interbred honeybees from Europe and southern Africa. Kerr was attempting to breed a strain of bees that would produce more honey and be better adapted to tropical conditions. The hives containing this particular Africanized subspecies were housed at an apiary near São Paulo, in the southeast of Brazil, and were noted to be hyper-defensive. A worker at the apiary removed a screen, resulting in the accidental release of the Africanized swarms that cross-bred with local European colonies. The descendants of these colonies spread throughout the Americas, moving through the Amazon Basin into Central America and reached Mexico in 1984.
The first Africanized bees in the U.S. were discovered in 1985 at an oil field in the San Joaquin Valley of California. Bee experts theorized the colony had not traveled overland but instead arrived hidden in a load of oil-drilling pipe shipped from South America. From the time of their escape to the present, the Africanized bees are credited with the deaths of over 1,000 humans, many of whom were operating noisy machinery near their hives or who had accidentally stepped on or near their ground burrows, causing an immediate defensive reaction. This security “kill zone” can extend outward for more than 600 yards, more than six football fields.
Examples of recent destructive invaders include the following: Dutch Elm disease (caused by the fungus Ophiostoma ulmi) is transmitted to trees by elm bark beetles. Since 1930, the disease has spread from Ohio through most of the country, killing over half of the elm trees in the United States.
Water Hyacinth is a beautiful aquatic plant, introduced to the U.S. from South America as an ornamental. In the wild, it forms dense mats, reducing sunlight for submerged plants and aquatic organisms, crowding out native aquatic plants, and clogging waterways and intake pipes. The Pale Cyst Nematode is a major pest of potatoes and related crops; uncontrolled infestations can reduce yields by 80%.
The Cane Toad preys on and competes with native species and is highly toxic to predators. But don’t forget to include an escapee from the domestic pet trade. Feral Pigs introduced for the sport of hunting, will eat almost anything, including native birds. They compete with native wildlife for food sources such as acorns. Feral pigs spread diseases, such as brucellosis, to people and livestock. E. coli from their feces was implicated in the E. coli contamination of baby spinach in 2006. One suggested method of controlling the exploding feral pig populations was the importation of a super-carnivore: the reptilian, blood-sucking, flesh-eating Puerto Rican chupacabra. Unfortunately, the chupacabra does not exist and neither does a quick fix for the feral pigs’ environmental damage and health hazards.
Good intentions alone cannot cure a damaged environment. To avoid unintended negative consequences, a thorough due diligence must precede any action that may modify the environment of a place or the introduction of non-native species. Otherwise, the “cure will certainly be worse than the disease.”
