Exotic Earthworms - University of Minnesota Duluth

Exotic Earthworms
Lesson Plan for 7th grade Life Science

This lesson plan borrows heavily from web materials at the Great Lakes Worm Watch website,
www.greatlakeswormwatch.org, and can be adjusted to different levels using the information
found there. Also recommended is the book “Earthworms of the Great Lakes,” by Cindy Hale,
ISBN 978-0-9792006-1-8.

Objectives:
Students will learn about earthworms as exotic species, and how earthworm invasion affects
nutrient cycling in forest ecosystems.
Students will gain field sampling experience and practice using dichotomous keys.
Students will work as a scientific team to set up and carry out an experiment.

State Standards:
7.I.B.1- “The student will identify questions that can be answered through scientific investigation
and those that cannot. The student will formulate a testable hypothesis based on prior
knowledge.”
7.1.B.2- “The student will recognize that a variable is a condition that may influence the outcome
of an investigation and know the importance of manipulating one variable at a time.”
7.IV.B.4- “The student will use and create dichotomous keys.”
7.IV.C.1- “The student will provide examples of the potentially irreversible effects of human
activity on ecosystems.”
7.IV.F.2- “The student will explain how energy is transferred through food chains and food webs
in an ecosystem.”

Day One: Nutrient cycling and Earthworm invasion

Bellwork: Reading (Introduction to Nutrient Cycling.pdf)

What is nutrient cycling?
Use slideshow (Nutrient Cycling.ppt) to review diagram from reading. Go over each step of the
process witgh students. Ask them to think of reasons why nutrient cycling is important?

What happens when nutrient cycling is altered in an ecosystem?
Discuss the introduction of earthworms. For information, consult the Great Lakes Worm Watch
website at www.greatlakeswormwatch.org. Photos in the slideshow are taken from this website,
and show visual comparisons of ecosystems with and without earthworms present. Ask students
to identify some differences between the photos. Refer back to the nutrient cycling diagram and
try to figure out where in the cycle the earthworms are having the greatest impact.

How do earthworms affect nutrient cycling?
Activity: Earthworm Invasion! (adapted from Great Lakes Worm Watch classroom activities)

Materials: green, yellow, orange, red, brown, and black construction paper
Game pieces (Earthworm_Game_Pieces.pdf)

String
Six clear cups or beakers

Heavy tagboard
Glue

Tape
50 Tootsie Rolls

Prep: Use tagboard and tape to make seven cubes, each 4 inches on a side. Print out game

pieces and affix to colored paper to color code each component in the nutrient cycling game.

(Suggestion: Use green for trees, yellow for plants, orange for forest floor, red for animals,

brown for soil, and black for leach.). Affix colored paper to the sides of the seven cubes as

follows:

Cube Station Sides

1 Trees 4 trees (stay), 2 forest floor

2 Understory 2 understory (stay), 2 forest floor, 2 animals

3 Forest Floor 2 forest floor (stay), 2 understory, 1 trees, 1 soil

4 Animals 3 animals (stay), 3 forest floor

5 Soil 2 soil (stay), 1 trees, 3 forest floor

6 Forest Floor 1 forest floor (stay), 5 soil

7 Soil 1 soil (stay), 2 tree, 1 understory, 2 leach

For explanations of the proportions of cube sides, see game instructions at

http://www.greatlakeswormwatch.org/educator/downloads/game%20instructions.pdf

Attach large station signs to appropriate colored backgrounds and use string and a hole

punch to turn them into signs which can be worn around student’s necks. Add ten Tootsie rolls

to each of five beakers or cups, leaving one empty.

Setup: Ask for five volunteers to be stations. The remaining students will be nutrient cyclers.

Each volunteer gets a station sign, appropriate cubes 1-5, and a cup of Tootsie rolls (nutrients).
Spread stations throughout the room or in a line at the front of the room. Go through each station

and explain the cubes to students and why each of them have the sides they do- this can be
related back to the diagram.

Play: Round One of the game represents an ecosystem prior to earthworm invasion. Students

will start by dividing into five fairly equal groups and lining up with one group in front of each
station. The student at the front of the line rolls the cube like a die, and then takes a Tootsie roll

out of the cup. The student will put that nutrient packet into the cup indicated on the die and go
to the back of that station’s line. For example, if I am at the “Trees” station and I roll “Forest

Floor,” I would take one nutrient packet from the “Trees” cup and bring it over to “Forest Floor”
station, where I wold drop it in that cup and get in the back of that station’s line. If I instead roll

“Trees (stay)” at the “Trees” station, I would take a nutrient packet out, put it back in, and go to
the back of the “Trees” station line. Play continues this way throughout the first round. After

several minutes, ask students to stop where they are and notice how many nutrients are in each
station’s cup.

Round two of the game represents an ecosystem in which earthworms have invaded. For
round two, choose another volunteer to represent the “Leach” station, and give that student the

appropriate sign and an empty cup. Substitute cube #6 for #3, and #7 for #5 at the “Forest Floor”

and “Soil” stations. Ask students to identify the differences between the round one and round
two cubes, tell how these differences represent an earthworm invasion, and predict the course of
the second round.

Game play in round two is similar except that when a student rolls “Leach” at the soil
station, that student takes the nutrient packet over to the “Leach” station and is finished with the
game. Another option is to have the student eat the leached nutrient, thus removing it from the
system, and return the wrapper to the cup held by the “Leach” station volunteer.

Day One Wrap-up:
After round two of Earthworm Invasion, have students examine the cups at each station and talk
about the differences from round one. Was their prediction correct? Briefly explain earthworm
sampling techniques. Assign groups for the next day and ask students to come prepared to go
outside.

Day Two: Earthworm sampling and identification
Bellwork: Get into your groups and get your sampling materials together.

Activity: Earthworm sampling
Materials: metal frames or sets of four stakes with string

dry mustard powder
empty gallon jugs
water
shovels
hand lenses
large plastic bins or buckets
Prep: Find places to sample, preferably on the school campus. Lawn areas or shrubby young
forests work well. If not using frames, cut string to lengths to make similar-sized sampling plots.

In-class: Explain sampling procedures and earthworm ecotypes. Ask students to make some
predictions about what they will find, and whether they might find different types of worms
using different techniques.

Sampling: Follow directions for liquid extraction, hand sampling, and flip & strip techniques,
outlined at http://www.greatlakeswormwatch.org/research/methods_worms.html
It is nice if students within each group get a chance to do all three sampling methods. Try
assigning different methods, then having them switch and teach each other the methods they
have already done.
Bring earthworms and some soil back into the classroom for identification and making
observatories.

Activity: Earthworm identification
Materials: dichotomous key to earthworm groups (Earthworm key.pdf)

rulers
hand lenses

Prep: Divide earthworms up so students can look at them in pairs. Give each pair of students
some worms, a key, a ruler and two hand lenses.

Identification: Look for a clitellum, which only the mature earthworms have. Separate those
without a clitellum- we will not be able to identify these in this lesson. Identify adult worms
according to ecotype, and set aside some worms for the observatories.

Day Two Wrap-up:
Ask students what they think of the worms they found, and whether their previous predictions
were correct. Ask them to be thinking about what other questions they’d like to have answered
about earthworms.

Day Three: Building earthworm observatories
Bellwork: Now that we have some earthworms and we have some idea what they are all about,
what are some questions you want to know about them? Write three questions.

What do we want to know about earthworms?
Ask students to share their questions, and as each one is shared, students should add it to their
own lists. Students may shout out answers to questions or may say things like “that’s a dumb
question,” at which point students should be reminded that for now we are just asking questions.
Once everyone has filled up a page with questions, tell them we have done one of the most
important jobs of a scientist: asking questions.

Which questions can scientists answer?
Go through the list of questions and ask students how they might get answers to those questions.
Are some questions more answerable than others?

How do scientists get answers to their questions?
Use this to talk about experimental procedures. Students are probably already familiar with the
concept of a control. Review this as well as treatments, variables, and hypothesis. Ask students
to formulate a testable hypothesis about some of their questions. Steer them towards hypotheses
than can be addressed through observing earthworms under controlled conditions.

How can we answer our questions?
Activity: Building earthworm observatories
Materials: Two clear 2-liter bottles

Sand
Soil
Dry hardwood leaves
Masking tape
Clear tape
String
Markers- red and green
Worms
Balance

Clipboard
Data sheet (Earthworm Data Sheet.pdf)
Funnel
Small shovel
Rulers
Squirt bottle

Prep: (Note: This experiment in this activity is written in its simplest form, and can certainly be
adjusted to include more replicates, different combinations or numbers of worms, etc.) Read
observatory information at
http://www.greatlakeswormwatch.org/educator/activities_observatory.html.
Print out task cards, and make extras of some cards so that each student gets a card. Print out
data sheet (Earthworm Data Sheet.pdf), or prepare to tailor one to meet the needs of students’
own questions.

In-class: Point out that scientists often work in teams, and that’s what we will be doing in class.
Go over “treatment” and “control” in an experiment, as well as “variables.” Explain that we will
be building earthworm observatories and each person will have a task to do to build a control
observatory (without worms) and a treatment observatory (with worms). Divide the class into
Treatment and Control teams. Pass out the task cards.

Building: Students do the task assigned to them on the card, with the materials listed. As each
task is done, the observatory gets passed to the next numbered task. There may be time when
students are waiting to get the observatory, so it is helpful to have them do some other activity or
reading while they wait. At the end you should have completed control and treatment
observatories.

Day Three Wrap-up:
Show the completed observatories and find them a spot in the classroom, where they will sit
while students observe them. Talk about the data sheet and assign students to record data several
days each week. Review the class hypotheses and ask what sorts of observations we would need
to make to evaluate the hypotheses.

Eventually, (after a month or more), there should be enough data that students can
evaluate the hypotheses, and perhaps this can be developed into a written study with graphs and
tables, etc.

Introduction to Nutrient Cycling

Nutrients are the molecules that plants and animals need to make body parts like leaves, stems,
muscles and bones. In a forest ecosystem, nutrients travel through many different “homes” in a cycle,
as shown in the figure below.

Trees use their roots to take up nutrients from the soil and forest floor. If a nutrient gets put into
the trunk or limbs of a tree, it can stay there for a very long time- sometimes hundreds of years. If a
nutrient gets put into a leaf it returns to the forest floor every year in the autumn when leaves fall.
There are lots of leaves, so lots of nutrients move from trees to the forest floor each autumn.

Understory plants take up nutrients from the forest floor. They can keep nutrients in their stems
or roots for long periods of time (but not as long as a tree). Most understory plants shed their leaves in
the fall, so they return nutrients to the forest floor much the same way trees do.

Animals (including some insects) get nutrients by eating understory plants. Some of those
nutrients return to the forest floor in animal waste material (such as poop). Nutrients that an animal
doesn’t pass through as waste are taken up into its body tissues and bones, where they may stay until
the animal dies. When the animal dies, nutrients are returned to the forest floor during decomposition.

Nutrients on the forest floor usually need to change form before they can be taken up again by
plants. Bacteria and fungi help by slowly breaking down materials on the forest floor. Some of the
nutrients get washed down into the soil in a process called leaching. Sometimes they leach down so far
into the soil that plants’ roots can’t reach them, so they cannot be taken back up.

Nutrient Cycling: The flow of nutrients through a forest ecosystem



Worm Observatory Data Sheet Hour ________________

Hypothesis 1:________________________________________________________________________________________________

Hypothesis 2:________________________________________________________________________________________________

Hypothesis 3:________________________________________________________________________________________________

Date CONTROL TREATMENT Observations

Sand Soil Leaf Sand Soil Leaf
Thickness Thickness thickness Thickness Thickness thickness

Number of worms starting _____________________ Weight ___________________________ Date ______________
Number of worms ending ______________________ Weight__________________________ Date_______________

Animals

Understory
Plants

Soil

Leach

Trees

Forest Floor

Trees Trees Understory
(stay) Plants

(stay)

Trees Trees Understory
(stay) Plants

(stay)

Trees Trees Understory
(stay) Plants

Trees Trees Understory
(stay) Plants

Understory Animals Forest
Plants Floor

(stay)

Animals Animals Forest
(stay) Floor

Animals Forest Forest
(stay) Floor Floor

(stay)

Animals Forest Forest
(stay) Floor Floor

(stay)

Forest Forest Leach
Floor Floor
(leave game)

Forest Forest Leach
Floor Floor
(leave game)

Forest Forest Forest
Floor Floor Floor

Forest Forest Forest
Floor Floor Floor

Soil Soil Soil

(stay)

Soil Soil Soil

(stay)

Soil Soil Soil

(stay)