Live Earthworms
Name _______________
Skills:
- identifying anatomical structures of the earthworm
- organizing and analyzing data
Objectives:
- Infer how physical and behavioral characteristics of the earthworm reflect adaptations to its
environment.
- Describe how an earthworm responds to light and moisture.
Purpose:
In this lab, you will look at live earthworms, observe their external structures, and test their
responses to environmental stimuli.
Background:
Earthworms are classified as annelids, or segmented worms. They have digestive, circulatory, and
nervous systems. Gas exchange is through the skin. They live in rich soil, which they eat, digesting
Anterior
the organic matter in it and passing the inorganic dirt particles out of the body. Earthworms are
not very mobile animals. They spend their lives in one small area and as a result do not encounter
many other earthworms. Their reproductive strategy is well suited to this type of life. Each
earthworm is a hermaphrodite, that is, it has both male and female sex organs. Thus, any individual
earthworm can cross fertilize with any other earthworm it encounters.
Procedure:
1. Moisten a paper towel, and place it in a clean dissecting pan. Place the worm on the paper towel.
You are working with a live animal. Handle it gently, and follow all lab instructions carefully.
Watch the worm move, and notice which end leads. The worm’s leading end is its anterior end.
Identify the worm’s posterior end, that is, the end away from the leading end.
2. To differentiate between the worm’s dorsal (back) and ventral (stomach) sides, roll the worm
over. Describe the worm’s response to being put ventral side up.
3. Notice how the body of the earthworm is divided into segments. Starting at
about segment number 32 there is a thickening in the body, called the clitellum,
as shown in the diagram below. The clitellum produces a mucus sac in which the earthworm deposits
its eggs.
Why do all earthworms have a clitellum?
4. Using bristles called setae, located on its ventral surface and sides, the worm moves through the
soil. Setae give the worm traction. Use a hand lens to examine the worm’s body and locate the
setae. You can also use your fingers to locate setae by touch.
Posterior
How many pairs of setae are on each segment?
5. To determine if the earthworm is sensitive to light, cover the beam of a flashlight with two
pieces of red cellophane. Fasten the cellophane in place with a rubber band. Darken the room, and
shine the beam on the earthworm. Record your observations of how the worm reacts to red light in
the table below
6. Replace the red cellophane with two pieces of blue cellophane. Shine the blue beam on the
earthworm. Record your observations in the table on the preceding page.
7. Remove the cellophane. Shine the light first at the worm’s anterior end, then on its middle, and
then on its posterior end. Note the worm’s responses. Shine the light on one area of the pan. See
if the worm will enter the spot of light. Record your observations in the table on the preceding
page.
How might this sensitivity to light be an adaptation to the earthworm’s way of life?
8. To determine whether an earthworm prefers a moist or dry environment, place a dry paper towel
next to the wet one. Place your worm across the two towels, as shown in the diagram below.
Wet towel
Dry towel
Does your worm move toward the wet towel or the dry towel? Why?
9. Place a piece of sandpaper next to the dry towel. Place the worm across the two surfaces,
anterior end on the sandpaper first. Observe the worm’s response. Then place the worm across
the sandpaper and dry towel, this time with the anterior end on the towel. Record your
observations in the table on the preceding page.
10. Look carefully along the dorsal side of the worm. You will see a thick purple line running down
the entire length. This is the dorsal aorta, the major blood vessel of the earthworm. Add cool tap
water (very little you do not want to drown your worm) to a large petri dish until the bottom is
barely covered. Place the earthworm in the dish, and observe it through a stereomicroscope. Look
for rhythmic contractions of the dorsal aorta. Each ripple of contractions represents a single
heartbeat. Determine the heart rate by counting the number of ripples that occur in exactly one
minute. Record the heart rate below. Now do the same for warm (not boiling hot you do not want
to fry your worm, unless you are going to eat it!).
11. Return your earthworm to the container in the front. Throw paper towels in the garbage cans.
Rinse dissecting tray and return it to the front of the room.
w
Name ________________________
Use the space below to answer the questions located throughout the procedure. Include the
question in your answer, so you know the question when you study for your test. There are 4
questions that you need to answer.
Heart rate:
Cool water ___________
Hot water _________
Analysis
12. Are any areas of the earthworm’s body more sensitive to light than other areas? Which ones?
13. Which kind of surface, the rough sandpaper or the dry paper towel, does the worm prefer?
Why do you think it prefers that surface?
14. Describe the relationship between temperature and heart rate in the earthworm.
15. What is the adaptive advantage of an earthworm’s response to light and moisture?
16. What is the adaptive advantage of an earthworm’s variations of heart rate as temperature is
varied?
17. Check the earthworm’s “robin response.” Gently grab a live earthworm’s anterior end as a robin
would. What is the worm’s response?
18. Design an experiment that would test an earthworm’s response to varying levels of moisture.
Describe the experiment in the space below.
Earthworm responses to Environmental Stimuli
Environmental
Stimulus
Response
Red Light
Blue Light
White light to anterior end
of body
White light to midpoint of
body
Approach/avoidance response
to white light
Moist/dry environment
Sandpaper/smooth surface
Label the clitellum, anterior, and posterior parts of the
earthworm.