Frequently Asked Questions about Invasive Species

What is an invasive species?

An invasive species is any non-native organism whose introduction can cause harm to the environment, human health or economic interests. Some of the invasive species on this website are already serious pests in North America, while others are not yet widespread.

How do invasive species get here?

Invasive species are introduced through many means. Intentional introductions have often been for agricultural or ornamental purposes. Once introduced, some of these species escape their enclosures or cultivation and can become established as viable populations. Accidental introductions are usually the result of contaminated freight or movement of contaminated wood products (including shipping pallets, bracing and other dunnage), plants, or food products. Individuals or propagules (including its seeds, eggs, spores, or other biological material capable of propagation) of these invasive species can be contaminants or hitchhikers in these shipments.

Are all exotic species invasive?

No, actually only a small percent of introduced species ever become invasive. However, it is nearly impossible to predict which species will become invasive and new species are being introduced every day. Some species are present for many years before they exhibit invasive characteristics. Many invasive species go through a "lag phase" in which their populations grow slowly until they reach a size large enough for the population to explode and/or become adapted to the local environment and become invasive.

What type of harm does an invasive species do?

Since invasive species are in a new environment, free from natural predators, parasites, or competitors, they often develop large population sizes very rapidly. These high populations can out-compete, displace or kill native species or can reduce wildlife food and habitat. Some also have the potential to disrupt vital ecosystem functions, such as water flow, nutrient cycling, or soil decomposition. Other invasive species cause massive amounts of economic damage to the agricultural business by destroying crops and contaminating produce. Some invasive species can cause direct harm to humans or domestic animals.

Why are the species on this website of concern to North America?

The species listed on theis website have the potential to create significant damage or harm through direct losses to crops, forests, landscapes, man-made structures and aquatic environments. These species can also cause environmental damage through wide-spread plant mortality. The presence of these pests may also result in quarantines being implemented by the US or other governments that restrict the import and export of a commodity.

Most of the species listed in this website are not native to North America. Native species can be pests but the introduction of exotic species has the potential to cause greater damage due to the lack of effective biological control agents and the lack of resistance in our native plants.

Why don't our native plants have resistance to these exotic pests?

Plants developed resistance to pests through their interaction with the pest over many generations. The plants that were resistant survived to pass their survival characteristics on to the next generation. As a result, the plant species develops a set of effective defenses that allows the species to survive. When a new pest is introduced, the defenses of the plant are not prepared to counter the attacks of the new pest; therefore significant losses are often experienced.

What type of damage do these species cause?

Pests can damage plants in many different ways. They can cause direct damage, such as tunneling by wood boring insects can led to the death of the plant, or indirect damage, where the injury inflicted by the pest weakens the plant and renders it susceptible to other stress factors. The type of damage can be diagnostic in the identification of the pest.

What can I do to fight these exotic pests?

The simplest and most important thing anybody can do to help fight invasive species is to prevent its' introduction and establishment! Invasive organisms can easily be transported on living plants or fresh products such as fruit. Many pests can be found in recently killed plant material including firewood, lumber, and wooden packing material. Avoiding the long range movement of these materials is a simple way to slow the spread of pests. Buying only certified pest-free nursery stock is also a good idea.

It is important to educate yourself and keep up to date on the status of these and other pests. Resources are available through your local extension office and on the web at and other websites. These resources have information on how to identify and control exotic pests that have already been introduced. By knowing what to look for and rapidly identifying any new introductions, we may be able to minimize the impact of new invaders. Report any occurrence of invasive species to your local county extension agent, state forestry agency, or to other federal or state natural resource or agricultural agencies. Spread the word; tell your neighbors if you see invasive species on their land. Volunteer with natural resource agencies to control invasive species. Control of small infestations is more effective and economical than trying to control a well-established, rapidly spreading infestation.