Lesson Plan

Pest Invaders: The Fight to Stay Native


The history of life on islands is a story of invasions. Ever since the high islands of American Samoa rose out of the sea as barren piles of volcanic rock, living things have been making the long and dangerous journey across the Pacific to reach this new land. Until a few thousand years ago, every plant, insect, and bird that lived on our islands was the descendant of a lucky adventurer that had crossed hundreds or thousands of miles of open ocean to establish a new colony here.


Students will be able to:

1. Define the vocabulary terms invasive species and conservation.

2. Identify four pests and explain their negative impact in American Samoa's ecosystems.

3. Describe how our actions can threaten the health of our ecosystems.
4. Learn about the role of the National Park of American Samoa in conserving our natural ecosystem.



Some changes have benefited some wildlife species. For example, the introduction of several important food plants such as breadfruit and bananas provide a year-round source of food for some birds and fruit bats, rather than seasonally like some native plants that are eaten by wildlife. Since the arrival of Europeans and Americans, the rate of introduction of new plants and animals to American Samoa has increased tremendously. The results have often been disastrous.

Some plants brought by the Polynesians “escaped” to spread widely through the natural forest such as ifi and nonu trees. More recently, about 250 alien plant species (many of them weeds) have also become established in American Samoa and some of these threaten our native forest. One that is familiar to everyone is the “mile-a-minute” vine, or fuesaina (Mikania micrantha). This was introduced by accident, sometime before 1924. It is now a major pest in plantations and forests, and has spread tremendously following tropical cyclones in the early 1990s. The vine needs sunlight for its very fast growth, and so doesn't do well inside the shade of the mature forest. The cyclones, however, opened up the forests to sunlight by knocking down many trees and breaking off the tops of thousands more. Vines like these can form layers several feet thick that can choke the seedlings of native trees and slow the recovery of our forests from the damage of the cyclones.

Another well-known pest to agriculture is the giant African snail (sisi aferika, Achatina fulica). This was reportedly introduced to the Pacific when the governor of Tahiti imported them to satisfy the hunger of his mistress for escargot, or edible snails. Bad, bad idea—not only was the snails not edible, but they quickly spread throughout Polynesia, and became a major pest of taro and other crops. Unfortunately, the story does not end there. In the hopes to control the giant snails, a predatory snail (Euglandina rosea) native to Florida was deliberately introduced here in 1980. The idea was that this new snail -- the one with the long pinkish shell — would kill off all the giant snails. Instead, it has driven the native land snails of the Pacific islands to the edge of extinction. Most of the native snails of Tahiti are now extinct, and the Samoan snails, which used to be collected by the thousands to make ula, are almost gone.

Meanwhile, the giant snail continues to thrive despite the new predator. Another example is of an invasion that is still under way—by introduced birds. There are two introduced bird species on Tutuila. These two species both arrived in the 1980's and there seems to be no name for them in Samoan. These are the Common Myna and the Jungle Myna.

They look almost the same—both are blackish brown, with big white patches in the wings and tail when they fly. They are now abundant from Pago Pago to Leone and have spread to the eastern and western ends of the island. None of these three introduced birds has made it to Manu'a, which is still home to only our native Samoan birds.

What's wrong with having new kinds of birds to live in our villages and gardens? In some parts of the world, including Hawaii, both bulbuls and mynas are serious pests on fruit crops such as guava. Second, they may spread the seeds of pest plants, like mile-a-minute vine, that native birds do not eat as readily. Third, they may drive out native birds. Finally, the introduced birds may spread diseases that will attack our native birds.

Another familiar pest in American Samoa is the cane or marine toad (Rhinella marinus), which is a relatively recent introduction to American Samoa. It was purposely brought here from Hawaii in 1954 to control mosquitoes or insect pests that attack taro. Toads (lage) were introduced into artificial ponds. The toads then expanded their range to include all of Tutuila, from sea level to the top of Mt. Alava.

The toads breed year-round here. All they need is standing fresh or slightly brackish water in which to lay their eggs. Thousands of eggs that look like a string of black and white pearls are laid by each female. Within a week the eggs hatch into small black tadpoles that feed voraciously on aquatic plants. The tadpoles look defenseless but are thought to be toxic to birds and other animals. Within a month these tadpoles develop legs and change into adult toads.

As adults, they typically hide under boards or vegetation during the heat of the day and emerge at night to feed on insects and other invertebrates. They eat snails, millipedes, centipedes, spiders, roaches, moths, flies, caterpillars, termites, beetles, ants, earthworms, grasses, and even an occasional small toad.

To some people it might appear that the toad is beneficial. One must keep in mind, however, that many of those insects would have been eaten by native birds. No one has examined the actual impacts the toads are having on our native wildlife, but there are many examples of introduced species causing the extinction of native plants and animals by out-competing them for food or other resources.

Another concern involving the toad is its toxic skin glands. The adults have two large parotid glands on their “shoulders” that secrete a creamy white fluid when handled. These secretions are highly toxic if eaten, rubbed into the eyes, or brought into contact with mucous membranes. Dogs have died when they mouthed these toads. In addition, a high incidence of the salmonella bacteria occurs in toads, thus an abundance of toads near drinking water supplies may lead to bacterial contamination.

The lesson to learn from these examples is that we must be very, very careful when thinking about introducing a new plant or animal to Samoa. Even species that seem beneficial, like the predatory snail, can have bad and unforeseen effects. And once a new species is established, it is almost impossible to get rid of. Wisely, the territory has established strict laws against bringing in exotic animals and any plant that may become a noxious weed. American Samoa's forests and wildlife are unique to the entire world, having developed here over hundreds of thousands of years in isolation. We must take care to preserve and protect this special heritage by staying alert to keep unwelcome invaders from our shores.


1. Glue
2. Flash cards
3. Hole puncher

4. String and/or plastic ribbon
5. Pencils and/or pens

6. Markers
7. Scissors

Handouts & Worksheets
1. "Pests" Handout



Introduce Inquiry Questions?

What are invasive species? How do they affect the ecological balance of American Samoa’s ecosystem?



Ask: Can you name any pests that you may have come in contact with on a daily, weekly, or monthly basis? Where and when did you encounter these pests? Have you ever heard the term invasive species? If yes, what and how did you hear about it? If not, what do you think it means? Wait for a response from students which may include mosquitoes, cockroaches, centipedes, etc. Explain that invasive species refers to a wide range of living things like trees and animals that do not belong in an area. Tell students that ecosystems with invasive species can cause a high level of imbalance between them and the native plants and animals that live in that area. Introduce students to four pests found in American Samoa by distributing the “Pests” handout.

Ask: Have you ever heard the term conservation? If yes, what and how did you hear about it? If not, what do you think it means? Explain that conservation means to protect something important from being destroyed or overused.” To illustrate the concept of conservation, show students the images of the National Park of American Samoa’s terrestrial crew eradicating invasive trees to conserve the native rainforest. If students have difficulty with the concept, give the example of their favorite toy and how they would clean and protect it from being damaged by other kids. Because the toy is of great personal value to them, the same is true with conserving our very own native fauna and animals that are of great economic, cultural, and social importance to all of those who call American Samoa—Home.

Activity 1: “Pests" Pocketbook

1. Introduce students to four pests found in American Samoa by referring to the “Pests” handout. They will see what these pests look like and learn about the harm they cause to American Samoa’s ecosystem.
2. Distribute flash cards, string, glue, and scissors. Have students use the scissors to cut out the photos of the different pests from the “Pests” handout. Use glue to attach these photos to the flash cards. Use a marker to write the name of each pest above the photo on the flashcard, and on the back, have students use pencils and/or pens to write a brief description of how and why that pest is not welcome in American Samoa. Caution students to be careful when handling the glue and scissors.
3. Take the hole puncher and create two holes at the top ends of the flash cards with the pest photo facing towards the student. After creating the two holes at the top ends, cut two pieces of string and/or plastic ribbon and insert into the two holes and then tie them into a knot.

4. Ask students to use markers to design their flash cards. They can write key words that describe the pest on each flashcard to make it more personal (i.e. bad, unwelcome, nasty, etc.).
5. Gather students as a group and review what they have learned about the different pests by having them share to the class their personalized “Pests” pocketbook. Make sure that students understand that they can carry these pocketbooks around with them so that they can easily identify invasive species in and around their environment.

Watch Video

Have a class discussion about how we might negatively affect our ecosystems in terms of native species and conservation. Ask the following questions:
1. In the video, what key factor is contributing to the faster spread of invasive species? What makes an organism invasive?
2. What can we do to help prevent the spread or the accidental introduction of invasive species?

Conclusion with Inquiry Question

What are invasive species? How do they affect the ecological balance of American Samoa’s ecosystem?


Stewardship Message

Encourage your family and friends to conserve, preserve, and protect our natural resources by becoming familiar with invasive plants and animals and reporting them to the local quarantine office. Do not bring into the territory any exotic plants and animals!