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Activity Guide
Invaders: Decisions! Decisions!


  • Create scenario cards that focus on local species.
  • Have the teacher conduct the post- role-play discussions as follow-up back in the classroom.
  • Have students perform their skits for public visitors.


Play the part of community decision-makers trying to take action on alien species.


Students will:

  • Identify several methods for controlling alien species.
  • Explain controversies and considerations surrounding the economic, ecological, ethical, social, and aesthetic issues involved in controlling alien invasions and restoring native species.


Social Studies, Science, Art (drama), Language Arts


alien species, ballast water, ecological restoration, exotic species, introduced species, invasive species, non-native, species


2 to 3 sessions


Copies of Scenario Cards


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

  • Standard F: Science in Personal and Social Perspectives—Risks and benefits


In recent years, scientists have shown that invasive alien species are one of the most significant causes of species extinctions around the country and the world. Not surprisingly, then, a great deal of effort has gone into trying to prevent new invasions and control those that have already occurred.

In general, preventing an alien invasion is less expensive than combating one that is already well underway. Preventive approaches include customs inspections at airports and seaports, treatment of the ballast water in ships, bans on dumping bait or aquarium fish into waterways, and so on.

Prevention techniques are sometimes controversial. In the United States, nurseries and pet shops will often oppose restrictions on certain plant and animal imports because these restrictions limit the stores’ opportunities for sales. In recent years both groups have begun to encourage voluntary control of invasive species as reflected in the pet industry’s Habitatitude program and the landscape and nursery industry’s support of the voluntary codes of conduct found within the St. Louis Declaration. (See the MORE INFORMATION section for details). Likewise, many people have challenged policies requiring ships to exchange their ballast water out at sea, pointing out that it can be hazardous to the people on board because it makes the ship unstable.

But the most intense controversies—and the most significant costs—generally arise over efforts to control alien species invasions once they occur. For one thing, control techniques are far more radical than prevention: They include tactics such as trapping invasive wildlife, introducing new alien species to control existing ones, and poisoning waters where aquatic aliens have invaded.

These techniques are often very expensive. They can also be objectionable to local people who have come to appreciate the alien invaders for their aesthetic, recreational, or nutritional value. And these methods are often filled with scientific uncertainty. For example, biologists concerned about purple loosestrife invasions in U.S. wetlands have begun introducing an alien beetle that is known to feed on loosestrife in the plant’s native habitat. Although scientists have conducted rigorous laboratory tests, many people worry that the beetle itself may end up becoming a nuisance in its new environment.

Despite all these challenges, most conservationists agree that controlling alien invasions and restoring native species is essential if we hope to sustain the nation’s—and the world’s—biodiversity. With that in mind, this activity gives your students a chance to explore some of the many approaches that people are taking to control invasions and restore native ecosystems. It also encourages them to grapple with some of the many complexities involved in these efforts.


Make enough copies of the Scenario Cards so that each scenario goes to one-fourth of the students.


1. Discuss alien control efforts. Ask the students if they have thought about what can be done to reduce the impact of alien invasions. Can they think of ways that people can prevent alien invasions from happening in the first place? Have they heard of any methods for stopping alien species invasions once they have already occurred? Explain that they will be taking a closer look at ways to control alien species in this activity.

2. Explain to the group that they will be acting out four true stories of conflicts involving alien species management. Divide the students into four teams and have them gather in different parts of the room. (Note: “Swan Song” is written at an easier reading level and describes a less complex issue than the other three.) Give each member of Team 1 a copy of Marina Sauce , Team 2 a copy of Ballast-ing Acts , and so on.

Have the team members read through their scenarios. Then have them come up with a skit, as directed on the cards, and assign roles to different members of their group. Ideally, all students should be involved in the role-play. Tell the students to try to develop a situation that will be dramatically interesting while getting to the core of the conflict described. (Note: As an alternative, you can have the students read and respond to their scenarios without having them perform. But role-plays often help get students involved in the material and provide an opportunity for interactivity with the entire class.) You will probably want to give the students at least 20 minutes to prepare their skits. Also have students indicate on a map the site or region in which their scenario takes place.

3. Conduct role-plays. Have the four groups take turns presenting their role-plays. After each performance, have the rest of the class jot down their answers to the following questions:

a. What is the non-native species described in the scenario, and what problems is it causing?

b. What actions have been proposed to control the invasive species?

c. Why do some people disagree with these actions?

When the students have completed their skits, have them return to their seats for a group discussion.

4. Discuss the complexities of ecological restoration. Remind your students that all four role-plays portrayed attempts at ecological restoration. Ecological restoration is the practice that includes restoring native habitats and species by combating invasives. Review the four scenarios and have students share their responses to the three questions. Then ask them what they would do if they were a decision-maker in each of these instances. Solicit feedback on one scenario at a time, asking for a show of hands for different options. Ask the students to explain their responses.

This discussion is an appropriate place to encourage students to listen to and show respect for differing opinions. You might want to see if the students can identify the values that inform their decisions in each of these cases. Did they find themselves most concerned about ecological health? Aesthetics? People’s welfare? Jobs? Costs? Why might it be useful to identify the underlying values of the different people involved in these conflicts before trying to reach a resolution?

5. Discuss scientific uncertainty. Ask the students to think about the role of scientific uncertainty in these disputes. In which examples did a lack of scientific certainty about the invasive species (and its effects) seem to affect the viewpoints of people involved? In which cases did lack of scientific certainty about ways to control the alien species play a role? Encourage the students to think about the pros and cons of taking action when you lack scientific certainty about the effects of that action.

6. Wrap up the activity. To wrap up this activity, have the students write a brief paragraph explaining whether they think alien species control is important and describing why it is often challenging. Then have them list explanations and examples of how alien species control can be a challenge:

  • economically
  • ecologically
  • ethically
  • socially
  • aesthetically

You might want to review these explanations as a group, or collect them to use as an evaluation.


Have students write a short reflective essay on a local non-native species. The essay should explore why trying to control this plant or animal might be controversial in economic, ecological, ethical, social, and aesthetic terms.

Needs Improvement—The essay includes some of the elements but fails to create a cohesive, reflective piece.

Satisfactory—The essay includes all of the required elements.

Excellent—The essay reveals critical thinking, logical reasoning, and creativity in how the elements are constructed.


  • Have your students investigate a local project to control alien species. What are the pros and cons of this effort? If your students can find people who support it and others who oppose it, have them interview both groups.
  • See if your students can find a local habitat restoration project that needs volunteers. Plan a weekend workday to help with this project.

Alien Species Resources

Here are just a few resources to help you design and enhance your Alien Species Scenario. Because this is an area of great ecological concern, there are many additional resources available on alien species.


Aquatic Plant Management Society, Inc. (APMS) is an international organization of scientists, educators, students, commercial pesticide applicators, administrators, and concerned individuals interested in the management and study of aquatic plants. The society published an activity booklet for fifth graders called Understanding Invasive Aquatic Weeds, which is available on line. Click on “Publications” and then on “Activity Book.” www.apms.org

National Invasive Species Council (NISC), formed by an Executive Order of the President in 1999, ensures that federal agency activities dealing with invasive species are properly coordinated. A comprehensive online information system can be found at www.invasivespecies.gov

National Sea Grant College Program has an Exotic Species Resource Center that produces educational materials. Sea Grant is a program of the National Oceanic and Atmospheric Administration of the US Department of Commerce. The New York Sea Grant program operates the Aquatic Nuisance Species Clearinghouse, an international library of research, public policy, and educational publications that pertain to invasive marine and freshwater aquatic nuisance species in North America. To access the clearinghouse visit www.cce.cornell.edu/aquaticinvaders/nan_ld.cfm or access the general Sea Grant College Program site at www.seagrantnews.org/education

US Environmental Protection Agency and the Ocean Conservancy highlight ways for volunteers to monitor invasive species and collect samples in their jointly produced Volunteer Estuary Monitoring: A Methods Manual. www.epa.gov/owow/estuaries/monitor/

Western Society of Weed Science (WSWS) is made up of weed science professionals working in the western United States and offers educational resources such as A Kid’s Journey to Understanding Weeds. www.weedcenter.org/education/kids_journey.htm

Curriculum Resources, Books, and Web Sites

Alien Invaders-A Rivers Curriculum Project investigates issues surrounding the zebra mussel, which has invaded the waters of the United States and Canada. Project materials and zebra mussel monitoring devices are available from the Rivers Project. www.siue.edu/OSME/river/Ordering%20Materials/Order.html

America’s Least Wanted: Alien Species Invasions of US Ecosystems, a program of NatureServe and the Nature Conservancy, provides a list of their “dirty dozen” alien species and describes the ecosystems these aliens affect. www.natureserve.org/publications/americasleastwanted.jsp

Black Sea Battle is a story produced by the Why Files in Education. The Why Files is an NSF-funded project that uses news and current events as springboards to explore science, health, environment, and technology with activities that are correlated to national science standards. Black Sea Battle tells the story of the invasion of jellyfish into the Black Sea and the resulting effects on the native fish population. www.whyfiles.org/055oddball/fish.html

The Bridge-Ocean Sciences Education Teacher Resource Center is a growing collection of the best marine education resources available on line. It provides educators with a convenient source of accurate and useful information on global, national, and regional marine science topics and gives researchers a contact point for educational outreach. Under the “Ocean Science Topics,” select “Biology,” then “Exotics.” Produced by Sea Grant Marine Advisory Services, Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 23062. www.vims.edu/bridge

Center for Invasive Plant Management, in cooperation with Montana State University, provides links to K-12 teaching resources on invasive species, including books and program ideas. The site is also a resource for invasive species grants, management ideas, identification information, and control methods. www.weedcenter.org/education/educator_res.htm#k12

Exotic Aquatics and Zebra Mussel Mania Traveling Trunks are part of the “Traveling Trunks” education program produced by the Illinois-Indiana and Minnesota Sea Grant Programs. Trunks are filled with educational materials that can be used by students to gain hands-on experience with aquatic exotic plants and animals. www.siue.edu/OSME/river/Ordering%20Materials/order_Zebra.html

Exotic Aquatics on the Move: Lesson Plans (for grades 6 through 12) is a collection of activities focusing on non-native species in the marine environment. The resource is available on CD-ROM and in print from Washington Sea Grant Program Publications. (206) 543-0555. www.seagrant.umn.edu/pubs/mailorder.html

Habitattitude is a campaign to prevent aquarium hobbyists, backyard pond owners, water gardeners, and others who are concerned about aquatic resource conservation from releasing aquarium and pond exotics into the wild. A partnership of the US Fish and Wildlife Service, Sea Grant, and pet and nursery industry groups. www.habitattitude.net

The St. Louis Declaration includes voluntary codes of conduct that help govern decisions made by commercial, professional, and government groups whose actions affect the spread of invasive plant species. These include government agencies, nursery professionals, the gardening public, landscape architects, botanic gardens, and arboreta. The declaration was the product of a three-day meeting in December 2001 that brought together experts from across the globe to St. Louis, Missouri to explore and develop workable, voluntary approaches for reducing the introduction and spread of non-native invasive plants. The Missouri Botanical Garden and the Royal Botanic Gardens, at Kew Gardens in England, convened the workshop. www.fleppc.org/FNGA/St.Louis.htm

The Sea Grant Nonindigenous Species Site (SGNIS), produced by the Great Lakes Sea Grant Network, is a national clearinghouse for information on zebra mussels and other aquatic nuisance species. www.sgnis.org

Wild Things 2001: Investigating Invasive Species is a middle-school curriculum guide created by the US Fish and Wildlife Service. The guide emphasizes field trips and outdoor activities as a way to learn about alien species in natural habitats. www.wildthingsfws.org/WT2001/guide_instructions.htm

You Ought to Tell Somebody! Dealing with Aquatic Invasive Species video gives an overview of the invasive species problem and provides identification and natural history information about one significant northwestern threat, the Chinese mitten crab. Available from Oregon Sea Grant, 322 Kerr Administration Building, Oregon State University, Corvallis, OR 97331-4501. $18.95. www.seagrant.oregonstate.edu/sgpubs/multimedia.html


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

Note to Teachers: This lesson and others relating to National Geographic’s Strange Days on Planet Earth can be found online at www.pbs.org/strangedays/

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