Lesson Plan 2 - Identifying an Earthworm

Students participating in the National Worm Survey must use the Key to Reproductively Mature Earthworms Found in Canada. Before going out into the field, Worm Watch suggests teachers and students spend one class period becoming familiar with a taxonomic Key. This investigation also helps to reinforce the vocabulary introduced in Investigation 1. It is also intended to encourage students to practice their science skills of observation and recording information.

This investigation is divided into two parts. In Part A, students use photographs on the Worm Watch web site to identify a known species of earthworm. Part A is designed as a tutorial to familiarize everyone with the Key to Reproductively Mature Earthworms found in Canada. In Part B, you will provide your students with the same species of earthworm. In this part of the activity, students use the Key to identify a living earthworm.

Key Concepts and Skills

Students will develop an understanding of the nature of science as well as the social and environmental contexts of science and technology.

Students will develop the skills required for scientific inquiry, problem solving, communicating scientific ideas and results, working collaboratively, and making informed decisions.

Students will construct knowledge and understanding of concepts in life science and apply these understandings to interpret, integrate, and extend their knowledge.

Students will be encouraged to develop attitudes that support the responsible acquisition and application of scientific knowledge to the mutual benefit of self, society, and the environment.

Key Terms

Taxonomic Key, prostomium, peristomium, body segment, genital tumescences (GT), clitellum, tubercula pubertatis (TP), setae, periproct, anterior, posterior, dorsal, and ventral

Additional Science Information

In this investigation students will use a taxonomic "Key" to identify or classify different species of earthworms. Students do not have to understand the modern classification system in order to participate in the National Worm Survey. Worm Watch, however, has provided the information below to give you a better understanding of the taxonomy and modern Classification. If you prefer, you can skip down to Using a Taxonomic Key section. It is up to you to determine how much of this information you want to share with your students.

As a result of the confusion using common names, scientists have designed a system to classify or group living organisms. Today, the modern science of grouping living things is called Taxonomy. Taxonomists put all living things into arbitrarily selected groupings or categories that lump the organisms together with other living things based on:

• Structural similarities and differences
• Genetic similarities and differences
• Biochemical similarities and differences
• Cellular organization
• Evidence from evolutionary relationships

Taxonomists group living things into a hierarchy that moves from general to specific. Organisms found in the same Kingdom are related, but not closely related. Presently, scientists accept that there are five Kingdoms of living organisms: Animalia, Plantae, Protoctista, Fungi, and Monera. The Animalia, Plantae, Fungi and Protoctista are part of the Domain Eukarya. The Kingdom Monera contains two Domains: the Eubacteria and Archea (www.kheper.auz.com/gaia/biosphere/ kingdoms). Currently, there is some of debate among scientists with respect to the Kingdom level of classification because the use of DNA-based technology has allowed us to look more closely at the genetic relationships between organisms.

Each Kingdom is divided into smaller groups called Phyla (singular Phylum) that contain more closely related organisms. Each Phylum, in turn, is subdivided into smaller groups called Classes. A Class is composed of many Orders, which contain a number of Families. A Family of living things is made up of Genera (singular Genus). Finally, each Genus is divided into the smallest and most closely related group of organisms called the species.

The smallest grouping in the taxonomy hierarchy is the species, which contains organisms that are very closely related. In order to be classified in the same species, the organisms must be able to produce viable (fertile) offspring. The species level is the most reliable and useful to scientists.

The following diagram illustrates the taxonomic relationships accepted by many scientists today:

The following table provides an example of the classification of two species of worms:

Table 1: Classification of the Dew Worm and Pasture Worm

Scientific Names

All organisms discovered to date have a two-part Latin name. For example, the scientific name for the dew worm is Lumbricus terrestris and the pasture worm is Aporrectodea turgida. The first name refers to the Genus of the organism while the second name represents the species name. The scientific name is always written in Latin and is either underlined or written in italics. The Genus name is always Capitalized while the species name is always lower case unless it is the name of the person that discovered and/or named the organism.

Earthworm Families, Genus and Species

Most of the earthworms that have been identified in Canada belong to one of four families. These families are the Lumbricidae, Megascolecidae, Sparganophilidae, and Octochaetidae. However, the majority of the earthworm species in Canada belong to the family Lumbricidae (Reynolds 1977). In Canada, the family Lumbricidae contains nine genera of earthworms, the genera Aporrectodea and Lumbricus are the most common. The following chart gives examples of some of the species in 3 of the 4 families found in Canada.

The Earthworm Field Guide in the Worm Watch Resources section identifies and describes many of the species of earthworms found in Canada.

Using a Taxonomic Key

In order to participate in the National Worm Survey, students should be able to classify or identify the earthworms in your area. To classify an organism, scientists use a tool called a taxonomic Key. A Key is a listing of specific characteristics such as size and body colour. The Key is based on a series of choices with each decision resulting in another choice until a result is reached.

Take a look at the Key to Reproductively Mature Earthworms found in Canada. The first characteristic of the worm your students will look at is Body Size. Students use the Earthworm Size Chart to determine if their specimen is a Small, Medium, or Large worm. There are three choices for this characteristic.

If the students choose Large earthworm, they work on the far right side of the Key. The choices for the next characteristic are based on Body Colour of the earthworm. Students decide if the earthworm is Dark Brown-Black, Red-Black, or Red-violet in colour. If it is not one of these colours, they would choose Other Colours on the Key.

Students follow the branches of the Key until they determine the Genus and species of their specimen.

Activity Preparation

Suggestion: Ask the students to bring worms from their garden or somewhere near their home where they have permission to sample. Then the students can practice sorting the earthworms into adults and juveniles. It is important to have adult earthworms for this activity so the students should try and bring a good selection of earthworms but at the same time try to minimise damage to the garden.

For this Investigation

Implementation Strategies

Go over the instructions with your students. You may have to read the instructions to younger students.

Use the Bookmarking or Favorite feature of your browser software to bookmark this activity on the Worm Watch web site.

Download and print the Key to Reproductively Mature Earthworms found in Canada. Provide one copy for every group of students.

Review the anatomy of the earthworm from Investigation 1 focus on the clitellum, and genital tumescence (GT).

Introduce students to scientific names (Genus and species). You may want to do a detailed discussion on classification systems or you may simply want to discuss the names of the earthworms. This will reduce the anxiety when students see words such as Lumbricus terrestris and Aporrectodea longa on the Key. Make sure students understand they do not have to learn or memorize these Latin names. However, they will be using the scientific names in the National Worm Survey.

Students should make an observation chart for the Online Worm or the earthworms illustrated on the Worm Watch poster provided by the Canadian Nature Federation (CNF) similar to the one shown below. They should also record each step and decision that they make using the Key. The chart and their notes will be the evidence they gather to support the identification of the worms.

The answers for the Online Worm Identification are provided for your information.

If the students follow the steps in the procedure, they will determine that the Online Earthworm is an Aporrectodea tuberculata.

Go over the instructions with your students. You may have to read the instructions to younger students.

Make sure they understand that earthworms should be handled carefully and treated with respect.

To make your life easier, you should have the entire class working with one species of earthworm. This will allow you to point out the characteristic features and all students will be able to follow your discussion.

Students should collect all of the materials before they are given the earthworm. Remind the students to keep their earthworms between the two wet paper towels throughout this investigation.

Follow the same steps as they did for Part A and complete the chart and record the steps and decisions they make while using the Key.

Hints and Suggestions

Place the students in teams of two. One person should be the observer and the second the recorder. The students should change roles periodically throughout the investigation. Encourage both students to be active participants in this activity.

Students should isolate the part of the Key that they are working on by covering the rest with a piece of paper. For example, if the worm is a Large worm, they should cover the references to Small and Medium worms. This will help keep them focused on the relevant part of the Key.

One student in each group should trace the steps they are using with their finger or lightly in pencil. This will help prevent them from getting lost. A HINT in the student document, suggests that they write down each step as they proceed through the Key. This will help them justify the identification of the worm. It will also make it easier for you to see where the students might have made a mistake using the Key.

Once again, earthworms do not like the light. Students should keep the worms between the two, wet paper towels as much as possible throughout the activity.

Caution students about a hand lens and the damage it can cause to their eyes as well as to the earthworm. Some students may have started a fire with a hand lens - you MAY want to use this as way to remind them about the dangers of looking at the Sun.

Caution students to wash their hands with soap and water when they are finished this investigation.

CAUTION: Do not add store-bought worms to the soil in your community. They may be an exotic species and compete with the indigenous worms in your area. If you do not want to keep the worms after this activity, put them into a plastic bag or a container in the freezer over night. The worms can be used for compost or fish food.

Wrap-Up

Students should return their earthworms to their container and clean up the mess.

Have each team of student discuss the evidence that they collected to identify their earthworm. Use any discrepancies as a starting-off point to discuss the value of careful observations and recording of information. Students should be encouraged to debate and discuss their results rather than being told that they are wrong (if in fact they did make a mistake).

Discuss why scientists use scientific names instead of common names of living things.

Review how to use a taxonomic Key.

Provide students with the opportunity to complete their drawings.

Extensions

Students design their own taxonomic Key to group common objects such as books in the library, geometric shapes, tree leaves, hockey/sports cards, or their music CD's. There are other fun activities about soil ecology and earthworms under Discover Soil.

ICT Integration

1. Design and develop a multimedia presentation that describes how to use a taxonomic Key.
2. Design and develop a web page based on the living earthworm they observed during this activity.
3. Use a scanner and graphics software to create the scientific drawings required to complete this investigation.

Cross-Curricular Connections

1. Make a model of their earthworm out of modeling clay or play-dough. Encourage students to place all of the structures they observed in the investigation on their model.
2. Write a poem or story about the earthworm they have observed.

Assessing Student Learning

Rubrics are rating scales commonly used to evaluate student performance. These scoring guides can be used to evaluate a wide variety of activities. They are quick and efficient methods of subjectively evaluating progress. However, you can make this form of evaluation more objective by making the criteria more specific. The more specific the criteria, the more feedback you will providing your students. The following is a sample rubric that you can use to evaluate the students in this activity.

Black Line Masters

• Blank Worm Diagram [48k PDF] Use the Key Terms in this lesson to label the parts of the earthworm.