What is an invasive species?

​

"Alien species are those that have become established outside their historical, natural range. Often these species are introduced by people, or they spread on their own. Most alien species cause little harm, or may be beneficial. When they cause harm to our environment, the economy, or to society, they are called invasive alien species, often shortened to invasive species." - NRCan, Adapting to climate change: The story of invasive insects in Canada’s forests