What defines an invasive species?
Written by
Kiana Okafor
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.An invasive species is distinguishably identified by two characteristics that are not up for discussion: it must be *non-native* to the ecosystem it invades and it must cause documented harm. Burmese Pythons in Florida are a perfect example. They are native to Southeast Asia and wreak havoc on native mammal populations. Zebra mussels similarly invade infrastructure while outcompeting local shellfish. If a species is not both foreign to the ecosystem, and it does not cause measurable harm, it cannot be considered "invasive".
Origin Verification
- Non-native status: Must arrive through human activity like trade or travel
- Introduction pathway: Documented history of transport (e.g., ballast water discharge)
- Genetic evidence: DNA analysis confirms foreign origins
Harm Documentation
- Ecological damage: Measured biodiversity loss exceeding native species impact
- Economic cost: Infrastructure damage or control expenses exceeding $1M annually
- Spread rate: Documented expansion beyond initial introduction site
Often, people struggle to distinguish invasive species from problematic native species. While white-tailed deer are a native species, they can become an issue without local predators. True invasive species, such as Japanese Knotweed, are dramatically different; true invasives lack any natural controls in their new environment. In field surveys, I've even observed Japanese Knotweed crack concrete foundations. The USDA uses particular and restrictive criteria in determining true invaders vs. nuisances that are native.
Prevention begins with correct identification. Verify the species against a legitimate resource, such as the USDA Federal Noxious Weed List. When you see unusual organisms, report them through EDDMapS. While working in conservation at Everglades National Park, I encountered timely public reports of python nests that helped us locate and intercept them. Your incessant vigilance protects local ecosystems from irreversible harm.
Read the full article: Comprehensive Invasive Species List
