Friend or Foe

Grade Levels



Students will
  • Define a pest
  • Identify pests and their biology
  • Identify beneficial and harmful effects of pests


Pests, Beneficial and Harmful Insects

Pa. Standards Addressed Doing the Activity

  • Teaching Methods  Assessment and Evaluation
  • Background Extensions
  • Getting Ready Resources

Pennsylvania Environment and Ecology Standards Addressed

  • 4.5.7. Integrated Pest Management
    A. Explain benefits and harmful effects of pests.

Other Pennsylvania Standards Addressed

  • Science and Technology
  • Teaching Methods
  • Observation, classification, investigation


  • 1 copy of Am I a Pest worksheet for each group
  • 1 copy of Are There Pests in My Garden worksheet for each student or group
  • Pencils
  • Poster materials – poster board, markers
  • Research books on insects, weeds, pests, gardening or have students visit the library


What is a pest? A pest is any living thing (plant or animal) that damages things we value, occurs where we do not want it, causes or spreads disease, or bothers us, our pets, plants or animals.  People don’t always agree on whether something is a pest.  Dandelion greens may be salad for one person’s dinner, but a pest in another person’s lawn.

Pests can be plants, insects, rodents, birds, bacteria, viruses, spiders, fungi, or other organisms depending on the situation.  Some pests were introduced to an area where they were not native.  The new area may lack parasites, predators or diseases that would naturally control the organism’s numbers.  If its population becomes too large, it can become invasive overwhelming native plants and animals or destroying their habitat.  Examples of introduced pests are Norwegian rats, garlic mustard, gypsy moths, and Japanese knotweed.

Plants and animals live in intertwined communities.  While we may consider something a pest, we must still recognize its role in the environment.  Pests can play important roles in cycles and foodwebs, acting as producers, consumers, or decomposers.  However, while termites decomposing dead trees are important to a forest ecosystem, termites decomposing your house may be a problem.

In some situations pest populations must be controlled.  Pests frequent an area because it provides for their habitat requirements. Modifying a habitat to make it less pest-friendly can help reduce their numbers and the chances that they will visit in the first place.  Learning more about the pest can also help you choose a control method that is least harmful to people and the environment.

In the garden, keeping plants healthy can help prevent pests.  Plants placed in the wrong location will not thrive and are more susceptible to problems.  Select plants that are suitable for your growing conditions and maintain healthy growth by watering, weeding, mulching and fertilizing according to the plant’s needs.

Getting Ready

Check the garden for signs of pests or pest damage, so you can direct students to these areas if they are having problems locating examples.

Doing the Activity

In the classroom
  1. Ask students the following questions:  What is a pest?  Why are they considered pests?  Explain that pests are things that bother us, damage things, make us sick, or occur where we don’t want them.  Ask students to give a few examples of pests. 
  2. Break students into small groups.  Give each group a copy of the Am I a Pest worksheet and a pencil. Have each group list any organisms they think might be a pest in the left-hand column under the word “Organism”.
  3. When students have listed their pests, have the first group read their list.  As an organism is named write it on the board and ask the other groups if they listed that organism also.  Keep a tally of how many groups listed the organism.  After the first group has finished have each group list any organisms that were not already mentioned. Continue until all organisms have been listed and tallied.
  4. Discuss which types of organisms (insects, weeds, etc.) were mentioned and which types were mentioned most often.  Usually insects top the list.  Mention some of the groups (bacteria, fungi, etc.) that students may not have included in their lists.
  5. Look at the top three organisms that were mentioned most often.  Ask students why these organisms were considered pests by most of their groups.  It is likely that they will be species that are most harmful or annoying to people or one that is found locally.
  6. For each organism that the group listed, have them give an example of a situation where the organism is a pest and not a pest. For example: 
    • Organism
      - Pest
      - Not a Pest
    • Bee
      - Stings us
      - Pollinates flowers
    • Mouse
      - Living in my house
      - Food for an owl
    • Termite
      - Eats houses
      - Decomposes dead trees
  7. After students have finished their lists, have them share some of their examples. Ask what the examples under the “Pest” column have in common.  Most likely they are examples that affect humans or something they value.  Ask what the examples under the “Not a Pest” column have in common.  These examples usually reflect the role the organism has in the natural environment or a positive use by humans – such as dandelions in salad. Explain that whether an organism is considered a pest depends on the situation.  While it may be harmful in one situation, it may also be beneficial in others.
  8. Ask students if we should treat the organisms they listed in the same manner wherever they occur.  If not, how would you determine when the organism is or is not a pest?
In the garden
  1. Take students to the garden. Explain that they will be examining the garden for organisms or signs of organisms - other than the plants that were planted there.   Discuss what the sign of an organism might be (castings, chewed leaves, droppings, etc).  Encourage them to look for both plants and animals.  Explain that they will be trying to determine whether the organism is a pest or not a pest.
  2. Ask the students how they might determine whether something is a pest or not?  Look for signs that it is damaging the plants (chewing leaves) or competing with them for space (weeds).
  3. Hand each student or group of students an Are There Pests in My Garden? worksheet and a pencil. Have students look for organisms in the garden.  They should list the organism, whether they think it is a friend (beneficial or non-harmful) or foe (pest), and give evidence to support their decision. For example:  organism – bee, friend/foe – friend, evidence – it was pollinating flowers.  Have them complete the worksheet for as many organisms as there is time. 
  4. Review student worksheets.  Encourage students to give specific examples of why they think the organism is a friend or foe.  If they noticed a sickly plant that had an insect on it, how would they determine if the insect was the cause?  If they see an organism that they consider a foe, what do they think the next steps should be? (Identify the pest, learn more about it, and monitor the population). 
  5. Ask students whether they think the garden has many pest problems. Why do you think we have pests in our garden? (Provides their habitat needs.) Are there any things that we could do to reduce the chances that pests will come to our garden in the first place? (Keep the plants healthy by selecting plants appropriate growing conditions, fertilizing, mulching and watering them)
In the classroom
  1. Give each student or group of students the name of a pest.  Include organisms that students listed as “foes” in the garden, if they were able to identify them.  The attachment Some Garden Pests is a partial list of common garden pests. You can choose additional organisms from it or come up with your own. Most garden books also have “pest” lists as well. 
  2. Tell students they will be conducting research to learn about their pest.  They should gather the following information: a picture of the pest, identifying characteristics, why it’s a pest, where/when it is found, what it eats or how it grows, natural enemies, and other interesting features or facts.  Have students visit the library or provide reference books.  Depending on their pest, students can find information in books on gardening, insects, plant diseases and pests, or weeds.
  3. Once they have gathered information, have them develop a Pest Profile poster.  Use the attached Pest Profile example or allow students to create their own format. 
  4. Have students present their poster to the rest of the class. Did any of the organisms that students listed as foes in the garden turn out to be friends?
  5. Ask students if they have ever taken any action to remove a pest?  Discuss some of the ways people control pests - pesticides, barriers, removal by hand, traps, beneficial insects, etc.  Discuss how these methods might affect the environment.  Are some methods safer for people, other animals, and the environment?


  • Review worksheets for accuracy of examples and evidence.
  • Review posters for accuracy and completeness.


  • Have students draw a garden foodweb that includes an organism they identified as a pest. Identify the producers, consumers, and decomposers. 
  • Have students research one organism they identified as a friend and one they identified as a foe to determine whether it supports their classification as a friend or foe. 


  • Ball, Jeff, Rodale’s Garden Problem Solver, 1988
  • Bradley, F.M. and Ellis, B.W., Rodale’s All-New Encyclopedia of Organic Gardening, 1992
  • Michigan State University Pesticide Education, Exploring Urban Integrated Pest Management, 2001
  • Project Food, Land and People, 2000



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