What Can We Learn About Invertebrates at the Pond?

• Lesson A - Presto Change-o
• Lesson B - Glorious Gastropods
• Lesson C - Spider Survey

Lesson A - Presto Change-o

FYI

Invertebrates are animals that do not have a backbone. About 97 percent of all animals on Earth are invertebrates.

The lessons in this Unit focus on aquatic larvae and nymphs of insects and spiders in the Phylum Arthropod, and snails and slugs in the Phylum Mollusk. In addition to these, there are many other kinds of invertebrates you can study in the classroom. You can get butterflies (larvae to adult), composting red worms, beetles, crickets, and snails in kits that include information, equipment, food, and the live invertebrates. You can buy these kits from biological supply companies (see Equipment and Materials Sources). They offer almost endless opportunities for learners to design inquiry investigations.

All insects (class Insecta) begin life as eggs. The eggs hatch and become immature insects. Many aquatic invertebrates that are collected for study are immature insects—either larvae or nymphs.

They live in ponds and streams until they are old enough to develop a full set of wings, fly off, and lay eggs of their own. Most insects go through a change in body type to become adults from the immature form. The change that larvae or nymphs go through is called metamorphosis. Metamorphosis takes place in different ways in different types of insects. In this lesson, learners compare two types of immature insects, larvae and nymphs, with the adult forms they become.

Most aquatic insect larvae are shaped like worms and have soft bodies; they look very different from the adult form of the insect. An insect larvae goes through complete metamorphosis to become an adult. An example that learners may recognize is the butterfly. Most learners probably know that the caterpillar, a wormlike larva, forms a chrysalis. While in the chrysalis, the caterpillar undergoes metamorphosis to become an adult butterfly. Then, the butterfly emerges from the chrysalis.

Examples of insects that live in water as larvae are mosquitoes, crane flies, dobsonflies, caddisflies, and midges. One interesting aquatic larva that doesn’t look like a worm is the water penny. Water pennies grow up to be beetles that live along the banks of streams.

Aquatic nymphs are different from larvae in one very obvious way. Instead of looking like worms, nymphs more closely resemble the adult insects. Their bodies are firmer than larvae and they have three obvious pairs of legs, just like the adult. Nymphs also are usually stronger swimmers. If learners look closely at a nymph, they will see wing pads (the beginnings of wings) on its back. As nymphs get bigger, the wing pads grow, and after metamorphosis, the adult has fully-developed wings.

MATERIALS

Part 1

• Ask learners to bring in photographs of their parents today and when they were children, and of themselves today and when they were babies.

Part 2 and Part 3

• Immature and Adult Aquatic Organisms (PDF - 14,301KB) cards, one set
• Quick Reference Guide to Aquatic Invertebrates (PDF - 4,340KB) cards, two sets

PREPARATION

Leaders should review the following:

• FYI section
• 4-H Science Inquiry Model
• Learner evaluation criteria in the ODE Scientific Inquiry Scoring Guide (PDF) to assist in coaching learners

Part 2

Photocopy the Immature and Adult Aquatic Organisms cards masters onto card stock. Cut out each card. Divide the cards into two piles, one for adult forms and one for immature forms of
aquatic organisms, and shuffle each pile.

Photocopy the Quick Reference Guide to Aquatic Invertebrates card masters onto card stock (if they have not been copied previously).

PROCEDURE

Part 1

Look at the picture pairs of the adults/children and children/babies. Lead a discussion of how and why living things change in shape and appearance as they get older and more mature.

Part 2

Lead a discussion based on the information provided in the “FYI” section about the body types of immature and adult insects. Learners should understand clearly the difference between a larvae and a nymph. Adapt the information to the age of the learners.

Hand out one of the Immature and Adult Aquatic Organisms cards to each learner in your group. Make sure that for every adult card you distribute, you also hand out the corresponding card for the immature form.

Ask learners to look for the card that matches the one they have, so that each pair of learners ends up with a card illustrating the adult and a card illustrating the immature form of an organism. To help learners match up forms with which they are unfamiliar, the shapes at the right edge (immature) and left edge (adult) of matching cards fit together to form a design.

When all the cards have been matched, have each learner pair describe to the group the immature and adult forms of their organism. For insects, identify the immature form as a nymph or a larva. Ask the following questions.

• Does any pair of learners have an organism that is not an insect? (Yes, the tadpole/frog cards.)
• Are any insects ever both a larva and a nymph? (No.)
• Which immature forms go through complete metamorphosis to become an adult? (The immature insects that are larvae go through complete metamorphosis.)
• Which immaturymphs form the second group. In these two groups, ask learners to consult their cards and look for other similarities among the insects pictured.e forms go through incomplete or gradual metamorphosis to become an adult? (The immature insects that are nymphs go through incomplete or gradual metamorphosis.)

Now, ask the pairs of learners to divide into two groups. Learner pairs who have immature insects that are larva form one group. Learner pairs who have immature insects that are n

Pass out a set of the Quick Reference Guide to Aquatic Invertebrates cards to each group. Ask them to use the cards to identify further the insects they have. (Note: There are no nformation cards for the water scorpion, tadpole/frog, giant water bug, water scavenger beetle, water penny, mayfly, or deer fly.) Can the learners discover which form of immature aquatic insect—nymph or larva— is more likely to be found in ponds rather than in streams?

The cards could be grouped as follows.

Lead a discussion about the similarities learners identified in the insects. Ask the learners to list some physical characteristics of the insects they think might help in classifying them. Ask older learners to design their own dichotomous key to classify the insects. (Remind them of the key to seeds they created in Lesson A - Seed Sense. There are two criteria listed at each step in the key.)

Ask each team to write down its key clearly on a piece of paper. When each group has finished its key, have the groups trade keys and insect cards.

Older learners can do some research to identify the characteristics of the insect orders listed above and then to determine whether any other members of these orders also have aquatic larvae.

Part 3

Ask learners if they think that the number or type of immature aquatic insects found in the pond is the same in all seasons of the year. (If learners began a long-term pond monitoring project after completing Lesson B - Water Quality Tests: pH, Dissolved Oxygen, Temperature, Sediments, they already will have some data available to answer this question.) How do conditions in the pond change with the seasons? Can learners make a connection between the results of any of the specific water quality tests and the number or variety of insects? Coach learners to determine how they may answer these questions using the 4-H Science Inquiry Model.

Create a timeline for the investigation. Learners will need to take samples in at least two different seasons of the year to provide a comparison.

EXTEND THE LEARNING

Project WILD Aquatic Education Activity Guide: Micro Odyssey

A Palette of Fun (4-H 713L): Pop-up Pizzazz

REFERENCE

This lesson was adapted from Pond & Stream Safari—A Guide to the Ecology of Aquatic Invertebrates, Cornell Cooperative Extension Publications. Used with permission.

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