Materials Included In Kit

Safety Precautions

Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

Disposal

The materials in this activity may be saved and reused for future classes.

Teacher Tips

• Enough materials are supplied in this kit for 5 groups of students. All materials can be reused.
• As an extension have students randomly take a sample of 10–12 of the macroinvertebrate cards and develop their own dichotomus keys. There are no right or wrong classification schemes. As long as they are dichotomous and follow a logical format, consider it a job well done. Students’ ability to formulate key descriptors of groups will vary considerably.
• Seeing the dichotomous grouping of the real objects makes the process more concrete than just reading or using a key.
• Have some biological keys available for student inspection after completing this activity. You might have students make a dichotomous key with living/once living items (e.g., leaves, insects), following the procedures outlined in this activity.
• Be sure to discuss some of the problems in making keys. Is there a right or wrong key? Are some keys better than others?
• What happens when a new organism is discovered? How is it incorporated into a key? How do biologists come to agree on key subdivisions? Or do they?
• After creating a dichotomous key, it is a perfect time to schedule a field trip and use dichotomous keys in the field. This is a great activity to perform before or during a water quality determination/actual macroinvertebrate sampling unit.
• Have students research other macroinvertebrates that are used to determine water quality.
• Flinn Scientific also sells a Stream Macroinvertebrate Sampling Simulation Kit (AP7401) that deals with the Biotic Index of water quality and mark-and-recapture techniques.

Answers to Questions

Macroinvertebrate Identification Sheet Set Key
See Teacher PDF.

1. What descriptions in the dichotomous key were most helpful in leading to identification?

   Student answers will vary.

2. If you were to create your own dichotomous key using the macroinvertebrates in this activity, what additional features or descriptions would you use?

   Student answers will vary.

3. Why are macroinvertebrates used to determine water quality?

   Macroinvertebrates are commonly used as indicators of water quality because they are sensitive to changes in the ecosystem, spend a large portion (if not all) of their lives in water, and they can be easily collected, analyzed and counted.

4. A specimen sample was taken from a local stream. The sample contained mayflies, stoneflies and waterpenny larvae. What might the presence of these organisms indicate about the water quality of the stream?

   Water that contains these pollution-sensitive organisms is most likely of high quality. These organisms cannot survive in polluted water.

Teacher Handouts

11047_Teacher1.pdf

References

EPA—Invertebrates as Biological Indicators, http://www.epa.gov/bioindicators/html/invertebrate.html (accessed June 2010).

Introduction

What are those insects and other organisms in the stream? In this activity, twenty illustrated aquatic macroinvertebrates will be identified using a dichotomous key.

Concepts

• Macroinvertebrates
• Classification
• Dichotomous keys

Background

Macroinvertebrates are organisms that have no backbone and can be seen without using a microscope. Aquatic macroinvertebrates are the organisms found in lakes, streams, ponds and other natural water sources. Macroinvertebrate life cycles go from the egg to adult form and can undergo either complete or incomplete metamorphosis. Complete metamorphosis has four stages—egg, larvae, pupa and adult. Macroinvertebrates that undergo complete metamorphosis include true beetles, flies and caddisflies. Many of these organisms are aquatic in the egg and larval stages and terrestrial in the adult form. Incomplete metamorphosis has three stages—egg, nymph and adult. Macroinvertebrates that undergo incomplete metamorphosis include mayflies, stoneflies, and dragonflies. Many of these organisms, such as dragonflies, also do not live directly in water as adults. Other species such as backswimmers and water striders spend their entire lives in the water. The length of the life cycle of a macroinvertebrate can vary from less than two weeks for some midges to two years or more for some dragonflies and stoneflies.

Macroinvertebrates are commonly used as indicators of water quality because they are sensitive to changes in the ecosystem, spend a large portion (if not all) of their lives in water, and they can be easily collected, analyzed and counted. Macroinvertebrates help maintain the health of water ecosystems by eating bacteria and decaying plant and animal matter. The quality of a body of water determines what types of organisms can live and survive in that water. Factors that affect water quality include dissolved oxygen levels, the amount of algae growth, pH, and the amount of pollution present. Macroinvertebrates such as mayflies, stoneflies and water pennies need high levels of dissolved oxygen to thrive. Finding large quantities of these organisms in water are generally an indication of good quality water.

Other macroinvertebrates, such as leeches and aquatic worms, can survive at lower dissolved oxygen levels because they can come to the surface of the water to obtain oxygen. Low dissolved oxygen levels are often associated with polluted waters while high levels indicate good quality water.

The sample macroinvertebrates in this activity will be classified using a dichotomous key. A dichotomous key is a flow chart that is used to help classify related organisms by sorting them into categories trait by trait with two different options given for each trait. For example:
2. A. Segmented legs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . go to 3
    B. No segmented legs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .go to 4

An option is chosen at each step (i.e., continue on to step 2 or step 3) and the dichotomous key is followed until the organism is correctly identified.

Experiment Overview

In this activity, 20 illustrated macroinvertebrates will be identified using a dichotomous key and a set of organism cards to learn more about the types of macroinvertebrates in our natural water sources.

Materials

Safety Precautions

Although this this activity is considered nonhazardous, please use all classroom or laboratory safety guidelines.

Procedure

1. Obtain a Macroinvertebrate Card Deck and an Identification Sheet Set.
2. Choose one of the Macroinvertebrate Cards from the deck.
3. Look at the dichotomous key on the Identification Sheet Set. The dichotomous key gives two options at each step. For example:

   2. A. Segmented legs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . go to 3

       B. No segmented legs . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . go to 4

   Choose an option at each step (i.e., continue on to step 2 or step 3).

4. Work through the key until the illustrated macroinvertebrate has been identified.
5. Place the card on the space next to its identification on the dichotomous key.
6. Repeat steps 2–4 until all of the macroinvertebrate cards have been appropriately placed on the Identification Sheets.
7. After all of the macroinvertebrate cards have been identified, review the correct placement and names of the macroinvertebrates with the instructor.
8. Answer the questions in the Post-Lab section.

1. What descriptions in the dichotomous key were most helpful in leading to identification?
2. If you were to create your own dichotomous key using the macroinvertebrates in this activity, what additional features or descriptions would you use?
3. Why are macroinvertebrates used to determine water quality?
4. A specimen sample was taken from a local stream. The sample contained mayflies, stoneflies and waterpenny larvae. What might the presence of these organisms indicate about the water quality of the stream?

Student Worksheet PDF

11047_Student1.pdf