What is an Invasive Species?


Invasive species are a major threat to biodiversity and the number one cause of extinctions to vertebrate animals. Invasive species threatened over three-quarters of the species listed as threatened or endangered under the U.S. Endangered Species Act.

But what, exactly, is an invasive species? In the United States an invasive species is defined as “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” So while not all introduced species are considered invasives, invasive species are all introduced, meaning they were brought in from somewhere else and are therefore not native in their new environment.

These invasive species can be introduced to new environments by many different ways, some accidental and some purposefully. Aquatic species can be inadvertently introduced to new waterways via the ballast in ocean going ships, insects can be introduced in packaging and wooden containers, and vegetation can hitchhike on boots, shoes, and other clothing. Other invasive species are intentionally introduced, such as the introduction of nutria to the Chesapeake watershed. Regardless of how these species are introduced, their impact on the environment can be catastrophic.

Many times an introduced species, such as the nutria, have few, if any, natural predators to keep their populations in check. As long as there is habitat and food their population can increase exponentially wreaking havoc on native species or ecosystem that has no built in checks or balances to keep their populations at a sustainable level.

Nutria - Damaging an Already Fragile Ecosystem

The nutria was introduced to the Chesapeake Bay watershed in the early to mid 1900s for their fur. After a decline in the demand for nutria fur many of the fur farms shut down and the nutria escaped into the wild. Having no natural predators in this new environment, and having plenty of food, these voracious feeders began to feed on the watershed’s native marsh grasses. The nutria tends to dig through the soil eating the soft roots and rhizomes eventually leading to barren sections of land that become susceptible to erosion. Any native animals that rely on these grasses for food or cover are then put at even further risk. Invasive species, when present together with other threats such as water pollution and climate change, often cause systems to become inhospitable to sensitive species.

While the nutria is one of the more notorious of the invasive species, it’s certainly not the only one. Zebra mussels, asian carp, snakeheads, and stink bugs are all invasive species and are all having a negative impact where they’ve been introduced. It’s estimated that the economic cost of invasive species in the United States alone is $137 billion per year.

Once an invasive species gains a foothold in a new area, the risk of that species spreading out to new locations is very real. Didymo, an invasive diatom in parts of the United States, spreads to freshwater streams and rivers by clinging to boots and waders in the infected water and then traveling to a previously uninfected waterway. The emerald ash borer, an invasive beetle from Asia, can make its way to new locations by hitching a ride in firewood that’s gathered in one place and moved to another. In these circumstances, no one is consciously moving these species around, but the effect is the same.

What Can We Do?

Invasive species are one of the biggest threats to biodiversity in the world. So what do we do? It’s obviously easier to simply not introduce an alien species than it is to rid it after it’s introduced, but in some cases it’s simply too late for that. The species is there and we now have to deal with it. How do we do that?

  • Keep it from spreading
  • Eradicate it from its non-native environment
  • Limit its impact on its non-native environment

The only way we can do these things is to know more about the species itself.

  • How did it get here
  • How is it doing
  • What is it doing
  • Where is it

Where do we go to find this information?

Introducing iMapInvasives

The NatureServe network has created an online tool for dealing with invasive species, iMapInvasives. iMapInvasives is an online database designed to manage and share invasive species information, this information is used by natural resource managers and citizen scientists, among others, to track monitoring and treatment efforts, and to stay informed of new invasive species.

The only way to reduce or eliminate the threat that invasive species pose to the environment is to have access to reliable and current scientific data. iMapInvasives gives us those data.