The cane toad was first introduced to Australia in the 1930s to help control pests in the sugar industry. It spread rapidly, out-competing native species and devouring native insect life.
On their home turf, plant and animal populations are kept in check by natural controls, like predators and food supply. However, when a species is introduced — accidentally or intentionally — into a new landscape that is not used to its presence, the consequences can be devastating. Most of these “non-native” species do not misbehave. But some non-native species spread unchecked by the lack of natural competitors and predators. They push out native species and cause ecological chaos. These are known as “invasive” species. All habitats are vulnerable to these invasions, from grasslands and forests to lakes, rivers and oceans.
How do invasions occur?
Invasive species are appearing around the world at an unprecedented rate and scale. Trade, transport and agriculture are three of the more common routes, or “pathways,” through which invasive species arrive.
Some invasive species are introduced through intentional actions that have unintended consequences: large and costly infestations of purple loosestrife, scotch broom and water hyacinth resulted from gardeners planting these species for their bright showy flowers. The cane toad was introduced originally in the 1920s and 1930s to control pests in agriculture and is now threatening native species from the Caribbean to Australia.
Other invasive species are spread accidentally: A Caspian Sea tanker dumped its ballast water — and the Asian zebra mussel — into the Great Lakes a little more than a decade ago. Now the tiny mussels threaten to smother 140 native mussel species, and waterfront industries, like dams and power plants, must pay billions in on-going repairs to clogged pipes while passing the cost to consumers. The Asian longhorned beetle hitchhiked to New York, New Jersey and Chicago in wood packing crates from China, where it escaped and has prompted the cutting, chipping and burning of over 8,000 street and yard trees at considerable cost. The beetle attacks maples and other hardwood species, threatening the timber, maple syrup, nursery, and fall foliage tourism industries across the Northeast.
By identifying the pathways through which invasive species arrive, action can be taken to prevent future invasions. The Nature Conservancy is working at national and international levels to identify these pathways and establish policies that help stop the spread of invasions without damaging trade.