In Wisconsin, invasive species are defined as non-native species whose introduction causes or is likely to cause economic or environmental harm or might harm human health. Invasive species disrupt and intrude on many aspects of our lives. They can crowd out or kill native plants and animals in waters, woods, prairies, parks, gardens and back yards. They can contaminate agricultural crops and, if ingested, may be toxic to livestock, pets and humans.

Several invasive species alter soil chemistry and slow plant growth. As plant composition is changed, populations of animals that rely on a plant species for food, cover or nesting sites are displaced. Invasive insects, such as emerald ash borer and Asian long-horned beetle, can weaken or kill trees through girdling and burrowing.

In addition, most people who enjoy the outdoors view invasive species as annoyances that make it more difficult to reach or enjoy the places they hold dear. In the absence of natural predators or controls, invasive species can overrun and blanket native species. They destroy parts of what make places special by altering the environment.

Outbreaks of invasive species are becoming more prevalent in news reports when they are first discovered or when they make the jump to a new area. Policy debates about them have recently gone all the way to the Supreme Court regarding closing locks in Chicago to prevent the spread of Asian carp into Lake Michigan. So many different non-native species have been documented on land and in water that you might think there is no hope that invasive species can be contained or controlled, but that is not the case for all species. Resource managers have made great efforts in recent years in learning the most effective ways to control some of these species. Preventing new species from getting established and slowing their spread are critical. Wisconsin now has a new tool to help do just that.

After five years of hard work, Wisconsin’s Invasive Species Identification, Classification and Control Rule (NR 40) became effective September 1, 2009. This rule was developed by a team of DNR staff specialists and the Wisconsin Council on Invasive Species working with an advisory group. They assessed species for possible listing in the rule and provided extensive opportunities for public comment, after which many revisions were made. This rule identified over 120 species as being invasive and grouped them as plants, fish and crayfish, aquatic invertebrates other than crayfish, terrestrial invertebrates and plant disease causing microorganisms, terrestrial and aquatic vertebrates other than fish, algae and cyanobacteria. Each organism was classified as either prohibited or restricted warranting different actions.

Prohibited species are those that are not yet known to be established in Wisconsin or are present in small infestations and, if reported, may warrant control efforts. These species would likely cause serious problems if left unchecked. As a prevention strategy, no person may transport, possess, transfer or introduce any of these species without a permit. When a prohibited species is found, the goal is generally to eradicate it if feasible or at least prevent it from spreading. Wisconsin DNR staff will work with the landowner to determine the best method of control and where possible, will seek to find funding, equipment, volunteers or other assistance to help with the control. Control of most invasive species takes several years, so monitoring the site and nearby areas is critical.

Restricted species are usually fairly widespread throughout a region or are found statewide and the chance of statewide eradication is low. Many of these species have already caused substantial economic and environmental damage. Some also harm human health. No person may transport, transfer or introduce any of these species without a permit with the exception of fish and crayfish. If a restricted species is present on your property, control is encouraged but is not required.

Some plant species are listed in both categories – restricted where the species is already established and prohibited in large portions of the state where it has not been found.

Reporting Invasive Species

If you suspect you have found a prohibited species, please contact the DNR invasive species team promptly. Send an e-mail to or call (608) 267-5066. Explain where you found the plant or animal, the population size, when you found it, and who owns the land (federal, state, other public land or private parcel), and tell us how we can contact you. It is also very helpful if you send pictures or a specimen of the species. With this information, the identification of the species can be verified and mapped.

Plant Species Regulated by the Invasive Species Rule (NR 40): DNR picture references for the Regulated Terrestrial Species.