What Are Invasive Species? Impacts, Examples, and Control

Defining Invasive Species

An invasive species is a non-native (exotic or alien) organism introduced — intentionally or accidentally — into an environment outside its natural range that causes, or has the potential to cause, significant ecological, economic, or public health harm. Not all introduced species become invasive; the vast majority fail to establish self-sustaining populations. However, an estimated 10% of introduced species establish populations, and approximately 10% of those become invasive — a pattern sometimes called the tens rule. Invasive species are recognized as one of the five primary drivers of global biodiversity loss, alongside habitat destruction, overexploitation, pollution, and climate change. The International Union for Conservation of Nature (IUCN) lists invasive species as a contributing factor in approximately 40% of animal extinctions since 1500.

Pathways of Introduction

Invasive species reach new environments through a range of vectors and pathways:

• Intentional introduction: Species brought for agriculture, horticulture, pest control, sport, or the pet trade — many ornamental plants, domestic animals, and sport fish were deliberately introduced and later escaped into the wild
• Ballast water: Ocean-going ships take on ballast water in one port and discharge it in another, transporting billions of microorganisms, larvae, and small organisms across ocean basins
• Hull fouling: Organisms attach to the hulls of ships and are carried to new ports
• Solid packing material: Wood pallets and packing crates harbor wood-boring beetles, nematodes, and other pests that spread through international trade
• Contaminated seed lots and soil: Agricultural trade inadvertently moves plant pathogens, weed seeds, and soil invertebrates
• Tourism and outdoor recreation: Hikers, anglers, and boaters transport seeds, soil, and aquatic organisms on equipment and footwear

Ecological Mechanisms of Harm

Once established, invasive species cause harm through several ecological mechanisms:

• Predation: Invasive predators kill native prey that lack evolved defenses; the brown tree snake drove 10 of 12 native forest bird species to extinction on Guam
• Competition: Invasives outcompete native species for food, space, light, or nesting sites; kudzu vine shades out native forest understory plants across the southeastern United States
• Hybridization: Some invasives interbreed with closely related native species, eroding genetic integrity; the barred owl hybridizes with the endangered spotted owl in North America
• Disease transmission: Introduced species carry pathogens to which native species have no immunity; chytrid fungus (Batrachochytrium dendrobatidis), introduced globally through the amphibian trade, has caused declines or extinctions in over 500 amphibian species
• Ecosystem engineering: Some invasives alter fundamental ecosystem processes — zebra mussels in the Great Lakes filter phytoplankton at rates that alter entire food webs, and invasive earthworms in boreal forests destroy the thick leaf litter layer that native plants depend on

Notable Invasive Species and Their Impacts

Economic Costs

The economic costs of invasive species are enormous and span multiple sectors. A 2021 study published in Nature estimated total global economic costs of invasive species at over $1.288 trillion between 1970 and 2017, with costs doubling approximately every 6 years. In the United States alone, invasive species cause an estimated $120–$137 billion in damages annually. Agricultural invasives — including invasive insects, plant pathogens, and weeds — account for a large share of these costs through reduced yields, increased pesticide use, and crop losses.

Control and Management Strategies

Successful Eradication Examples

Complete eradication of established invasives is rare but achievable, particularly on islands:

• New Zealand has eradicated invasive rats and stoats from over 100 offshore islands, enabling the recovery of kiwi, kakapo, and other flightless birds
• The screwworm fly (Cochliomyia hominivorax), a devastating livestock pest, was eradicated from the United States, Mexico, and Central America using the sterile insect technique — releasing millions of lab-reared sterile males
• Feral goats were successfully removed from Pinta Island in the Galápagos, allowing native vegetation to recover

Policy Frameworks

International instruments addressing invasive species include the Convention on Biological Diversity (CBD), which includes invasive species prevention and control in its Kunming-Montreal Global Biodiversity Framework targets. The International Plant Protection Convention (IPPC) coordinates phytosanitary standards for plant trade. The Ballast Water Management Convention (2017) requires ships to treat ballast water before discharge to prevent aquatic invasions. Despite these frameworks, enforcement gaps and the sheer volume of global trade and travel make preventing all invasions impossible, placing continued emphasis on early detection and rapid response.