Lesson Plan

Pest Invaders: The Fight to Stay Native

Overall Rating

Add your review
Grade Level:
Sixth Grade-Eighth Grade
Biology: Animals, Biology: Plants, Climate Change, Conservation, Ecology, Environment, Marine Biology, Wildlife Biology
45 minutes
Group Size:
Up to 36 (6-12 breakout groups)
National/State Standards:
Standard 6: Students assess the interrelated cycles and forces that shape Earth’s surface, including human interaction with Earth. (ASDOE Elementary Science Standards: Grade 4-8, pp. 40- 73)


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



Last updated: February 28, 2015