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Activity Guide
Invaders: America's "Most Wanted"


  • Provide background information on each “most wanted” species rather than having students conduct research.
  • Have the teacher conduct this activity before their field trip and then create the wanted posters during a visit to the informal institution. Exhibit the posters in a public gallery of “most wanteds.”


Track down information on one of several “most wanted” alien species and find out how it is causing problems in the United States.


Students will:

  • Define alien species.
  • Describe some environmental problems associated with alien species.
  • Give examples of several alien species that are causing problems in the United States.




alien species, biodiversity, ecosystem, exotic species, habitat, introduced species, invasive species, native species, non-native species, species


2 to 3 sessions


Copies (one per student) of handouts: America’s Most Wanted, The Plaintiffs and Case Profile

Educator Page: Answers to Student Handout "Case Profile"


This activity supports the following National Academy of Sciences Science Education Standards (Grades 5-8):

  • Standard C: Life Science—Regulation and behavior
  • Standard C: Life Science—Populations and ecosystems
  • Standard C: Life Science—Diversity and adaptations of organisms
  • Standard F: Science in Personal and Social Perspectives—Populations, resources and environments


For most people, the word “aliens” conjures up images of green-skinned creatures with antennas that invade Planet Earth from outer space. In the field of ecology, though, aliens are something much less extraordinary. They are the purple loosestrife growing in our marshes and lakes, the starlings pecking at our lawns and the zebra mussels clinging to piers in the Great Lakes and the Mississippi River. Generally speaking, alien species are organisms that have been transplanted to a new environment, intentionally or unintentionally.

Your students may not know much about alien species and they may not realize what a menace some of them pose to natural communities around the country and the world. This activity will introduce your students to some of the most meddlesome, invasive species found on land and in water in the United States. The activity will also help your students explore some of the native species that are being the most severely affected by alien invasions.


1. Make one copy for each student (or each team of students) of the America’s Most Wanted, The Plaintiffs and Case Profile handouts.

2. If you prefer to have students research local alien species, include several invasive species affecting your area on the list of “Most Wanted” species. Be sure to include a “plaintiff” species affected by each of these species. Arrange for students to have Internet access.


1. Hand out copies of America’s Most Wanted. Tell your students that this handout describes nine of the “most wanted” plant and animal species. What are these species? Why are they wanted? These are questions that your students, as bio-detectives, will have to figure out.

2. Distribute copies of Case Profile and The Plaintiffs. Explain to the students that their job is to do the following detective work: Gather information (individually or in teams) to complete a “case profile” for one of the “most wanted” species. Based on this information, students should be able to pick out which species on the “plaintiffs” list is being harmed by their “most wanted” species. Assign one “most wanted” species to each student or team of students. The students should gather information from books, magazine articles and the Internet. Although it will probably be easiest for them to search the Web using the name of their species as a search term, you may also want to direct them to the MORE INFORMATION section listed at the end of this activity.

3. Report with results. Have your students share the results of their investigations. Go through one “plaintiff” at a time and ask the students whose “most wanted” species are contributing to its decline. What can the group tell the rest of the class about the “most wanted” species that they researched? At some point, it should become clear to the class that all of the “most wanted” species have something in common. What is it? (Answer: They have all come — or have been brought — to the United States, or a particular part of the United States, from another country or region. All of them are harming species in their new environment.)

4. Discuss alien species. Explain to the group that these introduced species are called alien invasive species (see list, US Alien Invasive Species, for specific names). Review the definition of an alien species. (It is a species that has been transplanted into a new environment, either intentionally or unintentionally. For example, dandelions, ginkgo trees and oxeye daisies are all alien species: They originated on other continents and reached North America with the help of people.) Can your students think of any alien species other than those on the list you have given them? Explain that they may know this group of organisms by some of the other names used to describe them; for example, exotic species, introduced species, or non-native species. (Note: When using the term “alien” in this discussion, you should be careful to be sensitive to students who are legal or illegal aliens of the United States.)

Now explain that those alien species that are harmful to native species are called invasive aliens. Did the students realize that invasive alien species are causing so many problems for native species and native habitats? Explain to your group that invasive aliens are among the top threats to biodiversity-the variety of life on Earth. (You might use this opportunity to review the five greatest threats to biodiversity: Habitat loss, Introduced species, Population growth, Pollution and Over-consumption of natural resources. These threats can be remembered by the acronym HIPPO.) Some people think alien species are actually the biggest threat to Earth’s biodiversity. While not all alien species are destructive, the ones highlighted in this activity are among the most troublesome in our country.

Did the students find any information about the ways alien species affect humans? (Answers will vary). Your students will see that the biodiversity loss associated with alien species can have economic, social and even political consequences.


Have each student create a “most wanted” poster for a problem alien species that is not featured in the activity. (Refer to the MORE INFORMATION section and the US Alien Invasive Species list in this activity.) The poster should include a picture, the name of the species and basic information such as the background of the species, including its native geographic region and what kind of trouble it is causing. (The posters could also be placed in a gallery of “most wanteds” when completed.)

Needs Improvement—The species is not pictured or the information is only partially presented.

Satisfactory—The species is pictured and basic information is presented regarding the origin of the species and some of the problems it has created.

Excellent—The species is pictured with information about its origin (including the ecosystem), the regions of impact and the types of problems it is creating in these new environments.


  • Have your students gather newspaper, magazine and Internet articles on alien species.
  • Create an “invasive alien species” bulletin board to keep your group focused on the topic for the duration of the unit.


Invasivespecies.gov is the gateway to Federal efforts concerning invasive species. On this site you can learn about the impacts of invasive species and the Federal government’s response, as well as read select species profiles and find links to agencies and organizations dealing with invasive species issues. Invasivespecies.gov is also the Web site for the National Invasive Species Council, which coordinates Federal responses to the problem. www.invasivespecies.gov

The World Conservation Union’s Invasive Species Specialist Group (ISSG) Web site aims to reduce threats to natural ecosystems and the native species they contain by increasing awareness of invasive alien species and the ways to prevent, control, or eradicate them. www.issg.org

Weeds Gone Wild: Alien Plant Invaders of Natural Areas is a Web-based project of the Plant Conservation Alliance’s Alien Plant Working Group. This group provides information for the general public, land managers, researchers and others on the serious threat and impacts of invasive alien (exotic, non-native) plants on the native flora, fauna and natural ecosystems of the United States. www.nps.gov/plants/alien

The Nature Conservancy’s Invasive Species Initiative Web site is dedicated to protecting biodiversity and practicing weed management. The site provides weed control method handbooks, a comprehensive weed online database, a photography archive and gallery of pests and late-breaking invasive species alerts. tncweeds.ucdavis.edu

The Department of the Interior, US Geological Survey Invasive Species Web site contains comprehensive reports on specific invasive species across the United States with links to children’s pages and helpful teacher resources. www.usgs.gov/invasive_species/plw

A joint project of The University of Georgia’s Bugwood Network, USDA Forest Service and the US Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine (USDA APHIS PPQ), invasive.org is an excellent source of information and images of invasive and exotic species. www.invasive.org

The Animal and Plant Health inspection Service (APHIS) Web site outlines the US government actions to protect and promote US agricultural health, administer the Animal Welfare Act and carry out wildlife damage management activities. www.aphis.usda.gov

The Great Lakes Information Network (GLIN) Web site is a partnership that provides one place online for people to find information relating to the binational Great Lakes-St. Lawrence region of North America. GLIN offers a wealth of data and information about the region’s environment, economy, tourism, education and more. www.great-lakes.net/envt/flora-fauna/invasive/invasive.html

Hawaii is one of the most invaded places in the United States. The Web site of the Hawaiian Ecosystems at Risk project (HEAR) provides technology, methods and information to decision-makers, resource managers and the general public to help support effective science-based management of harmful non-native species in Hawaii and the Pacific. www.hear.org/AlienSpeciesInHawaii/index.html

The Protect Your Waters site is for all recreational users who want to help stop aquatic nuisance species. As Americans, we love to spend time in and on the water. Protecting these resources is an important part of our overall enjoyment. A concern we must all address is the spreading of harmful plants, animals and other organisms. These aquatic nuisance species can hitch a ride on our clothing, boats and items used in the water. When we go to another lake or stream, the nuisance species can be released. And, if the conditions are right, these introduced species can become established and create drastic results. This Web site offers ways to reduce the nuisances. www.protectyourwaters.net

The Web site of the Aquatic Nuisance Task Force is dedicated to the prevention and control of aquatic nuisance species and implementation of the Nonindigenous Aquatic Nuisance Prevention and Control Act (NANPCA) of 1990. www.anstaskforce.gov


The following is a partial list of troublesome alien species found in different regions of the United States.

Green crab, gypsy moth, purple loosestrife, Dutch elm disease, Hydrilla, mute swan, West Nile virus, European starling, hemlock woolly adelgid, Asian longhorned beetle

Green crab, melaleuca, water hyacinth, Chinese tallow, Hydrilla, English ivy, kudzu, fire ant, Brazilian pepper, nutria

Zebra mussel, rusty crayfish, sea lamprey, gypsy moth, purple loosestrife, Dutch elm disease, Asian longhorned beetle, leafy spurge

Scotch broom, green crab, Chinese mitten crab, goldfish, wild pig, Hydrilla, Africanized honey bee, fire ant, cheatgrass, bullfrog

Fire ant, Africanized honey bee, tamarisk

Mongoose, wild pig, wild goat, rosy wolf snail, invasive marine algae, giant African snail

Source: invasivespecies.nbii.gov


To understand the role people are playing in biodiversity loss, it helps to think of something called the HIPPO dilemma. This term does not refer to hippopotamuses; rather, it is an acronym for the main threats to biodiversity:



Activity adapted from Oceans of Life—An Educator’s Guide to Exploring Marine Biodiversity, a resource of World Wildlife Fund’s Windows on the Wild biodiversity education program. For more information on WOW please visit www.worldwildlife.org/windows

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