Worm
Hunt!
Collecting
and Observing Earthworms
Where will you find earthworms? They're in garden soil, vacant lots, lawns, parks, or pastures. A cool, moist fall day or evening is a great time to look for worms. Humid days before rains, or during rain showers are especially good for collecting worms. Fall is the best time to sample worms because most are sexually mature, which helps you tell who's who.
Bringing
Up the Worms
USDA soil scientist Dr. Dennis Linden tells one way to find worms: First, look
at the soil surface. Castings ("worm poop") are small piles or pellets
of soil, often mixed with some plant litter. Castings are signs that earthworms
are present. When you've found a likely spot for worms, dig a spadeful of soil
and sort through it for earthworms. With experience, you may also find cocoons.
While you are digging, always watch for evidence of large burrows with "slickened" walls.
These may indicate the presence of night crawlers--the larger, deeper-burrowing
earthworms.
Forest ecologist Cindy Hale gives directions for a method that will bring many
of the deeper burrowing earthworms to the surface. How many different kinds
of worms can you find in your study area?
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- Measure off a square of soil about one foot on each side for your "study area." Use string or boards to make boundaries around the area.
- Dissolve 1/4 cup (about 40 grams) of ground yellow mustard seed (this is dry mustard powder from the spice section in the grocery store) in one gallon of water. Shake it up well. (Recipe adapted from the SCPFRC)
- Slowly pour the mustard solution over the soil inside the boundaries of your study area. Pour it so it soaks into the soil instead of running off the soil. The worms will start coming up. Don't worry; while the mustard irritates their skin and makes them escape to the surface, it does not harm the worms.
- Pick up the worms with a forceps and put them right into a pan of fresh tap water to rinse off the mustard solution. Now you can take them out of the water, lay them on a wet paper towel, and use a magnifying glass for a closer look. Explain that the worms are "breathing" oxygen through their wet skin, so they must be kept moist at all times. Set out a few water misters for students to share. Explain that worms are fragile animals and can be hurt easily, so they must be handled with gentleness.
NOTE: Students may work in teams of two, with one student assigned as recorder. After oberving the worms for at least ten minutes, bring the class back together and ask teams to be ready to share their observations with the class.
- Using a magnifying glass, count the rings or segments along the length of a wormís body. These segments help the worm to twist and wiggle forward or backward with the help of hair-like structures called setae (pronounced SET tay).
- If you place the worm in a plastic cup or on a petri dish, you can see the underside (ventral side) or the worm. You will be able to see inside the worm, too. What can you see inside of the earthworm? Look for the heart and blood vessel. Look for the pulse, indicated by the vessel alternately swelling and contracting. Which direction is the blood flowing? How cold you take an earthworm's pulse?
- Find the anterior or head end, which is more pointed and narrow. You can also place the worm on a rough piece of paper and see which direction it travels. The head end usually goes forward first.
- On the head end of the worm, find the clitellum, a whitish, swollen band that looks like a collar around the wormís middle.
- Count the segments from the head/mouth to the clitellum. This number is different in different species, so counting segments can help you know whether your worms are of different species.
- Look for the hair-like bristles called setae around or under the worm's body. Worms use their setae to help crawl and also to grip and anchor themselves firmly in the ground. (Thatís why you see robins tugging to get worms out of the soil!) Are setae paired? How are they spaced around the body? What differences in setae patterns do you see?
- Look at the worm's shape. Is it cylindrical or flattened?
- Look at the top (dorsal) and belly (ventral) side. Try turning the worm. A worm turned over will immediately right itself.
- Notice the worm's color: brownish, reddish, or gray-blue, or pale or white. Pigmented worm species live at or near the surface of the soil in organic matter such as leaf litter or compost piles, but they may also burrow very deeply and feed at the surface on fresh litter. Nonpigmented worms live and feed in the soil, not at the surface. The litter-dwelling species help the soil-dwelling species because they work the organic matter into the soil where the soil-dwellers can eat it.
- Compare the worm's movements on wet and dry surfaces and it s response to water, touch, and darkness.
After you study and compare the worms, place
them where they can safely get back into the soil.
- Draw a large, simple outline of a worm on the chalkboard. Have students come up and draw, label, or make notes on the drawing to record their observations. The drawing can show the segments, clitellum, anterior and posterior ends, the heart and blood vessel, and setae. This diagram may help you.
- As a class, discuss how the earthworm's various structures and behaviors help it to survive in its underground home. After discussing the observations, introduce the term adaptation and help students define it (the characteristics and behaviors of an organism that help it to survive in its environment).
- Investigate more about earthworms with these recommended Web sites:
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