- Some species arrive in a new area through migration.
- Some are spread unintentionally by human activities. When people travel, they often inadvertently carry alien species along. For instance, insects may arrive in a new place by travelling on luggages.
- Some species are introduced on purpose as pets or to combat pests, which turn out to be invasive in the new place.
- Ships can carry aquatic organisms in their ballast water, while smaller boats may carry them on their propellers. Insects can get into wood, shipping palettes, and crates that are shipped around the world.
- Some ornamental plants can escape into the wild and become invasive.
- Illegal smuggling/trading of fruits and vegetables across borders can introduce not only potentially harmful new plant species but also any insects and parasites that may live in them.
- Higher average temperatures and changes in rain and snow patterns caused by climate change will enable some invasive plant species—such as garlic mustard, kudzu, and purple loose strife—to move into new areas.
Picture Credit : Google