In this lesson, students will create mini habitats to observe earthworm behavior and learn about the important role that earthworms play in decomposition and plant growth. Grades 6-8

decomposer: an organism that feeds on and breaks down dead plant or animal matter

decomposition: the process of breaking down or being broken down into simpler parts or substances especially by the action of living things (as bacteria or fungi)

fungi: spore-producing organisms that lack chlorophyll and often grow filaments (tiny root-like structures)

habitat: the natural home or environment of an animal, plant, or other organism

organic matter: a soil component derived from the decay of once-living organisms like plants and animals

This lesson is part of a series called, Too Much? Too Little? created to introduce middle school students to the connection between soil nutrients and the food they eat. The lessons consist of a series of demonstrations and hands-on experiments that show that plants require nutrients in certain quantities. The lesson series allows students to investigate soil properties, learn how to properly prepare fertilizer nutrient solutions, identify deficiencies in plant nutrients using a key, and much more. Other related lessons include:

• Plant Parts and Functions: Anatomy and physiology of a plant.
• Digging Into Nutrients: How plants obtain nutrients from the soil.
• The Right Solution: How fertilizer solution is properly calculated and applied.
• Can We Have Too Much of a Good Thing?: Effects of applying too much or too little fertilizer.
• The Right Diet for Your Plants: Read fertilizer labels and choose the best fertilizer.
• Let's Vote On It: How soil nutrients effect local communities and economies.
• It's a Dirty Job: How earthworms benefit soil.

Although they often go unnoticed, earthworms play a significant role in our lives. As decomposers, worms have the important job of recycling waste material into nutrients that plants can use to grow and provide food for people and other animals. As worms burrow through the soil, they ingest soil particles and obtain nutrition by digesting any dead plant or animal remains, fungi, and bacteria in the soil. Through this process, the worms mix up the soil, providing air spaces for roots and water to penetrate. Worm excrement, or castings, provide excellent fertilizer. This is why many home gardeners put worms into their compost piles.

If you have ever held an earthworm, you probably noticed that it was moist. Earthworms do not have lungs, they breathe through their skin, which must be moist in order for oxygen to dissolve and pass into their bloodstream. Earthworms need a cool, dark, moist environment. They do not have eyes but do have special receptor cells to sense ground vibrations and light. The rings on an earthworm’s body are called annuli. Tiny bristles called setae help the worms pull themselves through the soil. The lighter colored “bump” in the middle of the earthworm is the clitellum, the structure responsible for secreting mucous required for the worm to breathe, reproduce, and for protection as the worm burrows through rough soil. Worms have a special organ called a gizzard to help them grind up and digest the soil that they eat.

Earthworms come in a variety of sizes. The largest known earthworm species in Australia can reach nearly ten feet in length! Some worms live close to the surface of the soil, while others burrow six or seven feet deep.

Earthworms can be classified into three main groups based upon the soil areas where they prefer to eat and burrow.

• The worms you find in compost piles are in the Epigeic group. Epigeic earthworms live in plant litter near the surface of the soil and need a lot of decaying organic matter to feed on. These worms are relatively small and can tolerate living in conditions with many other worms. This makes them well suited for composting.
• Endogeic earthworms live in the upper-to mid-soil layers and feed on soil and decomposing organic matter. Endogeic earthworms don’t have permanent burrows.
• Anecic earthworms are deep burrowing and have permanent burrows that can be spotted by little piles of worm castings at the soil surface. These worms are large and are often referred to as “night crawlers.” Anecic earthworms feed on decaying vegetation that they pull into their burrows from the topsoil.

Earthworms are hermaphrodites, meaning they have both female and male reproductive parts. After mating, earthworms lay eggs inside a cocoon covering that hatches in about two or three weeks, but this can vary depending on species and weather conditions. Baby worms are called wormlets and look like tiny pieces of thread when newly hatched.

In addition to improving soil and decomposing waste, earthworms are important food for a variety of animals such as birds, snakes, amphibians, rodents, and other small animals.

1. Inform your students that you will be giving them a list of facts about one specific thing. Ask them to raise their hand when they think they know what you are talking about. 
2. Use the following clues¹:
   • They aerate the ground.
   • They are vital to soil health.
   • They can eat up to 1/3 of their body weight per day!
   • They are a source of food for animals like birds, rats, and toads.
   • They are typically only a few inches long.
   • They are capable of digging as deep as 6.5 feet.
   • They are commonly used as fishing bait.
   • They can also be known as "night crawlers" because they can be seen feeding above ground at night.
3. What is it? A worm! 

Several days before starting construction of the worm habitats, introduce the project to the class so students have time to gather materials from home. Have students bring plastic bottles, soil, and worm food as identified on the attached instruction sheet, Directions for Earthworm Habitat Construction and Observations. Students will work in pairs and should decide which partner will be in charge of providing the listed items from home.

During this introduction, brainstorm answers to the following questions with the class and keep a list of ideas on the board:

1. What would the world look like without earthworms?
2. What role do earthworms play in the ecosystem?
3. What do earthworms eat?
4. How do earthworms help plants?
5. How do earthworms help people?
6. What type of habitat do earthworms need?
7. How can we turn our food scraps into fertilizer?
8. How should worms be cared for during their stay in our earthworm habitats? (At the end of a two week period, worms will be released into the school garden).

Instruct students to transfer the notes from the class brainstorm onto the graphic organizer called, An Earthworm’s Dirty—but Important—Job. Also, have students fill out the Earthworm Project Agreement showing that they understand the rules for caring for the earthworms in the habitats the class will create. Discuss the rules as a class and collect the signed Earthworm Project Agreement.

Variation

• Instead of having groups of students create their own earthworm habitat, make one large worm habitat in an aquarium for the entire class to observe.

ELL Adaptations

• This lesson employs hands-on activities and cooperative learning. Activities provide opportunities for students to exchange, write, and present ideas.
• Provide a model of the finished worm hotel project so ELL students can see what their completed project should look like.

After conducting these activities, review and summarize the following key concepts:

• Soil quality is important to the growth of our food.
• Farmers maintain soil quality in many different ways. Earthworms are beneficial to the soil.

1. http://animals.nationalgeographic.com/animals/invertebrates/earthworm/

This lesson was updated in 2013 with funding from California Foundation for Agriculture in the Classroom and a grant from the California Department of Food and Agriculture’s Fertilizer Research and Education Program. The Fertilizer Research and Education Program (FREP) funds and facilitates research to advance the environmentally safe and agronomically sound use and handling of fertilizer materials. FREP serves growers, agricultural supply and service professionals, extension personnel, public agencies, consultants, and other interested parties. FREP is a part of the California Department of Food and Agriculture (CDFA), Division of Inspections Services.

Editor: Shaney Emerson
Executive Director: Judy Culbertson
Illustrator: Toni Smith
Layout and Design: Nina Danner
Copy Editor: Leah Rosasco

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