A native plant, animal, or insect species occur naturally in a region, while non-native species are introduced, usually by humans, from somewhere else either unintentionally or on purpose. A non-native species has to harm the environment, economy, or human health for it to be considered invasive. Some common invasive species in Illinois are zebra mussels, feral hogs, brown marmorated stink bug, and garlic mustard.
Once introduced, invasive species spread quickly and aggressively, often because they don’t have natural predators. They then compete with native species for resources.