Plants and animals have always traveled with us. The more we travel, the more species we unknowingly transport. Our transportation methods then become pathways for invasive species.

For example, birds or the wind may carry seeds from garden plants into the wild. Exotic pets escape or are released into parks, lakes, and rivers. People may carry seeds on their clothing, in suitcases, or on cars. Packets of birdseed may contain seeds of invasive plants. Solid waste and soil that have invasive plants may be dumped as fill into wetlands. Plant seeds, insects, small animals, and organisms may hide in ship cargoes or ballast water, on the outside of boats, and on planes.

There are many such pathways, some more important than others: