Documentary Lens Lesson Plan for Emergence of a Dragonfly

Documentary Lens Lesson Plan for Emergence of a Dragonfly Page 1

Documentary Lens Lesson Plan for Emergence of a Dragonfly

by William Scott

S.J. Willis Continuing School, Greater VictoriaSchool Board, SD #61, BC

Curriculum Connections

Emergence of a Dragonfly shows a time-lapse view of the final moult of an aquatic nymph as it transforms itself into an adult dragonfly. This metamorphosis, a process that in real time might take a couple of hours, is shown over a five-and-a-half-minute time period in the film. This silent film without commentary is an extreme form of observational documentary. It is introduced by a very brief on-screen introductory text. The running time is six minutes.

This lesson has been designed for the science curriculum in British Columbia. Along with tying in many of the general skills and processes of science such as observing, inferring or hypothesizing common to all levels, this film has curriculum links to Grades 2, 4, and 7 in Life Science, Science 10 in genetics, and Biology 11 for arthropods. Although these materials have been designed for the Grade 7 science curriculum, the nature of the film allows for teacher adaptation to other grades and subjects.

Related units of study: Science Processes; Body Systems: Reproduction, Growth and Change; and Ecosystems.

Lesson Objectives

Working in groups, students observe, analyze, and interact with a film on the incomplete metamorphosis of a dragonfly. Students will use qualitative and quantitative observations to describe the growth and development of a dragonfly using concepts of ratio and proportion. Examining the class results involves data analysis.

Through small group work, class discussion, readings and Internet research, students will explore dragonfly biology based on questions that arise from their own observations and interests.

Outcomes and Expectations

Students will:

describe the growth and changes in the development of an organism (Life Science: Body Systems - Reproduction, Growth and Change)
determine measures of central tendency for a set of data: mean (mode & median ) and range (Statistics and Probability in Data Analysis)
use text and electronic media features, including indices, tables of contents and keyword searches, to locate specific information (Comprehend and Respond: Strategies and Skills)
locate and interpret details in print and non-print media to gather information and build understanding (Comprehension)

Resources

The AES Bug Club for Young Entomologists

A Beginner's Guide to Dragonflies (A detailed article of six pages with adult dragonfly and damselfly diagrams)
Biokids: Dragonflies (Excellent readability containing background information and pictures)
Biology of Dragonflies and Damselflies
Diagrams of Dragonfly Nymphs (from Buglopedia)
Dragonflies and Damselflies
Dragonflies of the Family Aeshnidae in British Columbia: Biological Notes and Field Key, Based on Specimens in the Royal British Columbia Museum Collection
Introduction to Insects (on-line diagrams of dragonfly’s incomplete metamorphosis can be found at Gary A. Dunn’s useful site)
Buglopedia (from the New South Wales Department of Natural Resources)
Background on documentaries available in the “Behind the Camera” article at the Documentary Lens Web site.

Materials Required

Supplies per class: one rubber or latex glove (small size to fit student volunteer’s hand snuggly); scissors; chalkboard protractor and large ruler; chart paper and felt pens.

Supplies per student pair or triad: a calculator; pencil and pen; protractors and small plastic rulers (if students are working at a number of computer stations); and 20 cm string or a long pipe cleaner (not really essential items).

Activities for Emergence of a Dragonfly

Introductory Activity

Activating Prior Knowledge

Have students dedicate a page for their notes to the introductory activities. Write the following on the overhead or the board:

Just when the

caterpillar thought

the world was over

it became a butterfly. (Anonymous)

Ask the class to define “metamorphosis.” Review the concept together. Have the students make a list of changes that humans go through. The word meta is Greek for change of, and morphosis means form. In terms of insects, metamorphosis is a transition from one form to another, into an adult. Butterflies and their kin go through four stages of complete metamorphosis, transforming from egg to larva to pupa to adult. In incomplete metamorphosis, insects like dragonflies or damselflies change from egg to larval form (nymph) to adult, a three-stage life cycle.

Have students speculate about the importance of metamorphosis in our culture. You might want to mention a few current or ancient examples. For example, dragonflies in various Native cultures symbolize swiftness or agility and they are often connected to water, spring, fertility and/or renewal.

Brainstorm students’ current knowledge of dragonflies and their role in the ecosystem. Dragonfly biology is an excellent topic to introduce the class to the study of insects (arthropods) and/or pond ecosystems. Dragonflies belong to the insect order Odonata that also includes damselflies. Odonata is Greek for “toothed jaws.”

On the board, draw a timeline or circle representing a dragonfly’s lifespan of 1-6 years. Have students speculate as to how long each stage lasts and what the dragonfly might eat at each stage. Have students review the dragonfly lifecycle, and emphasize the following points:

After hatching from the egg, the larva or nymph, is aquatic. Eggs don’t overwinter; the larvae do.

The larva goes through a number of moults (usually 10-14).
Wing buds get larger with each moult.
Species vary in the length of time that they remain as larva, from 1-6 years.
Adult dragonflies in Canada live 1 or 2 months; if they’re lucky they reproduce.

The following points should emerge either now or during subsequent research:

The main predators of larvae are fish, frogs and diving ducks. Dragonfly larvae are carnivorous, and they tend to prey on the larvae of smaller insects, fish spawn and tadpoles. The larval stage can vary in duration from about 3 months to 4 or more years depending on the species and growth conditions (latitude, altitude and amount of daylight).
Adult dragonflies are often at the top of the pond food chain. They eat a large variety of flying insects (mosquitoes, midges, flies, bees and other dragonflies). Their main predators tend to be birds (red-winged blackbirds, purple martins, kites, kingbirds, moorhens or coots) or predaceous insects (other dragonflies or giant robber flies).

Review the following key terms: invertebrates, insects and exoskeleton. Using handouts and/or the overhead, review the main parts of insect anatomy, using diagrams of the larval dragonfly and the adult dragonfly.

Developing Understanding and Skill Activity

Step 1

To simulate the dragonfly’s problem of shedding its larval shell, ask for a volunteer with a “thick skin” to participate in a class demonstration. Ask the students for ideas as to why pulling ourselves out of our skin might be a problem for us. (Our skin tends to flake off in tiny pieces; for the most part, our skin layers are tightly bonded to each other.) What would we have to do before pulling ourselves out of our skin?

Have the volunteer put a rubber glove on one hand and then have him or her take off the glove without using a free hand, feet, or teeth. Students’ can provide suggestions. Once the student has removed the glove, discuss the similarities and differences in this model to the dragonfly’s problem.

Similarities: The rubber glove usually needs to be pressed against a substrate so that friction helps pull the glove off the hand. In the same way, the larva tends to attach itself to a plant or other substrate by means of its claw-like legs. It continues to grasp the substrate after the dragonfly has emerged and left. Also the more tightly the glove or larval skin is attached to the “body” inside, the harder it is to remove the outer layer.
Differences: The dragonfly has to make a split in the outer skin first, and it doesn’t pull itself out of its larval skin in the same manner. The rubber glove is more flexible than the larval skin. Also the dragonfly must “puff” itself up after emerging so that it has room to grow.

Step 2

Have students examine a larval dragonfly diagram to predict where the adult might emerge. (See Resources above)

Step 3

Explain to the class that they are going to be viewing the film twice.Ask students to jot down, in point form, the two most interesting sequences/events they observe, and to give reasons for their choices. Students should also list as many questions as they can think of regarding dragonfly biology.

Questions can focus on anything researchable: from factors that affect larval/adult dragonfly development to dragonfly senses and behaviour to dragonfly interactions in the ecosystem. Each student should aim to generate a minimum of 12 questions, and then pick the three that they find the most intriguing and record them. The questions should be phrased so they encourage detailed answers rather than yes or no responses. For their most important questions, students should predict or speculate about some possible answers.

For example, what factors determine when a dragonfly emerges or moults its exoskeleton? Student predictions might include hormones, length of daylight, food eaten, and/or water temperature. How does a larva or adult detect, catch, and eat its prey? Student predictions might include sense of smell/vision, mouth parts, and clawed legs working together.

Finally, students are to give their overall impression of the film.

Step 4

Ask the class to think about how they could use the film to measure any growth of the dragonfly as it emerges. The actual length of the dragonfly larva in the film is probably 2.5-4 cm. Suggest that the magnified versions in the video are in the same proportions to the real larva.

Tell students to try to watch the film from two perspectives: as scientists and as documentary filmmakers. As scientists, they will measure the lengths of various body parts to compare their relative lengths in the larva and adult dragonfly. This type of measurement is often done in seeking ways to distinguish different species from each other. On their diagram of the larva, they are to locate the exact place it pulls itself out of its old exoskeleton.

As filmmakers, they will describe the sequences as extreme close-ups (ECU) of single body parts, close-ups (CU) of two body regions, or full shots (FS) showing the entire dragonfly.

Step 5

Have students view the video a second time to complete their descriptions of the main action occurring in each scene on the student video log sheet.

If you are using a VCR/monitor, stop the video after the following sequences: #4, #5, and #6 to allow students the time to complete the video log and to carry out the measurements required to complete the relative size of body parts. Review #4-6 with the class, so they feel comfortable with the process.

Use the attached teacher program logas a guide for times/events. Return to scene 4 and have a pair of volunteers make measurements from the classroom VCR monitor or have pairs of students at a computer complete the measurements in teams. Each student should measure the larva using a length of string or a pipe cleaner, and then use a ruler to determine the actual length in centimetres. (Clear plastic rulers are harder to read if used by themselves. If students take their measurements independently, they will be more likely to catch errors. In pencil, students should complete the appropriate section of the relative size of body parts versus leaving the calculations for a later time.)

Note

The Worksheet Video Log for this lesson includes suggested responses. You will likely want to remove some or all of the suggested answers in the “Type of shot,” “Text on screen or scene description and action in scene,” and “Questions about the biology of dragonflies that come to mind as you watch the film.”

Step 6

If pairs of students have their own computer, they could continue the process and complete the Worksheet Video Log. If you are using a VCR in front of the class, you might want to be more selective and restrict the number of scenes you have students review (sequences 11-12, 17-20, 22, and 24 would work well). Measurements of the adult dragonfly are required in scene 24 to complete the relative size of body parts.

Post-ViewingActivity

“Have students work together in small groups to decide on their six most interesting questions about dragonfly biology (collected from individual students’ lists of top three questions in Step 3 above). They are to write their questions on chart paper (if possible, post the chart paper around the classroom). By random allocation, make different groups responsible for reporting back to the class on each topic area.”

Worksheet Video Log for Emergence of a Dragonfly

Name ______Date ______

Sequence number and time / Type of shot (ECU, CU, FS) / Text or scene description and action / Questions about the biology of dragonflies that come to mind as I watched the film
#1
0:00 to 0:06 / Text appears: “The National Film Board of Canada presents A FRAGMENT OF LIFE”
#2
0:06 TO 0:33 / Title of film appears: “Emergence of a Dragonfly” There are three stages in the development of a dragonfly: the egg, the nymph, and the adult insect; this is called simple or incomplete metamorphosis. / If the larva is aquatic, how does it move around, catch its prey, get oxygen?
How and when does it prepare for the transition to life on land? What specific changes occur? What controls the timing of the change?
#3
0.33 to 0:50 / In the change from the aquatic nymph to the airborne adult, the skin splits away along the back and the dragonfly struggles out.
The film has no text from here on. / What changes occur in the dragonflies skin to allow it to moult like this?
DNA? Hormones?
#4
0.53 to 1.06 / FS / Sideview from left-hand side of larva. The larva is gripping a plant stalk with its legs. The abdomen of the nymph appears to flick upwards in an arch 4 times. This segment ends with an ECU of the head thorax area of the larva viewed from the left-hand side. / Is the flicking a method of making sure the new adult is totally separate from the old larval skin or shell? Or is it a byproduct of filming?
#5
1:06 to 1:20 / CU / View shifts to another close-up of the back (dorsal side of thorax) and head. A split in the larval skin occurs just above the wing buds on the thorax. / What part of the adult will emerge first?
#6
1:20 to 1:50 / CU / From a slight sideways view the split appears to be triangular and widens. “Shoulders” (top of thorax) of emergent adult are visible. / What causes the larval skin to break? Is the thorax swelling? Are these segments shown in real time?
#7
1:50 to 2:00 / ECU / Focus on legs that appear crab-like. The legs appear to be pulsing slowly out. / Are the adult legs soft when they emerge? Is the dragonfly able to use them at all?
#8 and 9
2:00 to 2:13 / CU side to FS dorsal / Head and thorax from left side. The adult shoulders are visibly free, and the head is arching forward. Left eye of the adult becomes visible. Ends with dorsal view with head completely free. / Would the dragonfly be able to see or respond to predators at this point?
#10
2:13 to 2:22 / ECU / Side view of the head. Mouth parts are visible and moving, legs emerging, head slowly moves away from the larval shell to go off-screen. / If this film is 6 minutes long and the process takes over an hour, what parts of the process did the filmmaker cut?
#11
2:22 to 2:27 / FS / Side view. Emerging adult looks like a racecar driver leaving his car, legs moving slightly with one leg almost free. (Note: what appears to be white cord-like tissue is not a leg.) / Is the dragonfly motionless for most of the time that the director films? Does it have to rest or wait? Why?
#12
2:28 to 2:36 / ECU / Side view of leg slowly emerging. First pair becomes free. / What predators do dragonflies have?
#13
2:36 to 2:48 / CU / Top view. Upper body moves backwards. Two front legs point upwards as the second pair of legs becomes free. / How many cameras did the filmmaker have to use? Is this film constructed from filming one dragonfly or many different dragonflies?
#14
2:48 to 3:00 / ECU / Side view of second pair of legs being freed. (Note: what appears to be white cord-like tissue is not a leg.) / The emerging dragonfly seems very flexible. Does the exoskeleton harden quickly or slowly?
#15
3:00 to 3:12 / FS / View of the emerging adult arched backwards and downwards away from the larval shell. The right leg of the final third pair of legs is freed. / What scientific experiments have been done to understand the hidden processes we are seeing?
#16
3:12 to 3:19 / ECU / Close-up of head and first pair of legs. Mouth parts moving / Do dragonflies have antennae? What are they used for?
#17
3:19 to 3:24 / FS / The adult abdomen has been freed significantly, as compared to sequence #15. Note the relative size and length of the wing buds.
#18
3:25 to 3:40 / CU to FS / A close-up of the abdomen and the third leg switches to a side view. In a contortionist move, the upper body and legs flip towards the larval shell. The front legs appear to grasp the head region of the larval shell; the second and third pair grasp the abdomen and substrate respectively. / Do all dragonflies do this the first time? Do some have to try several times?
What would happen if the dragonfly was prevented from performing this motion? Would it still be able to remove itself?
#19
3:40 to 3:49 / ECU / Side view of the head of the young adult with two pairs of legs attached to the head region of the larval shell. The third pair are on the substrate. The abdomen appears to get pulled out of the larval shell in pulses as the adult pushes its body forward against the resistance of its legs. / Is it possible to develop and raise millions of dragonflies as mosquito control devices?
It seems like the dragonfly is using a significant amount of effort. It must still be a fairly tight squeeze.
#20
3:49 to 3:55 / FS / Side view of the adult as the last part of the abdomen is pulled free and extended downwards.
#21
3:55 to 4:08 / CU to ECU / A head and thorax side view switches to a dorsal or top view of the lower thorax , showing the wing buds.
#22
4:08 to 4:29 / CU / A sideview close-up of the lower thorax, wing buds, top of the abdomen is intercut with a CU of the head. The main action is the time lapse growth of the wings with the abdomen appearing to ‘pulse.’ Count the number of segments in the abdomen. / If this whole process takes an hour or two, how do the wings expand so rapidly? Are the wing cells growing rapidly? Are they being inflated with blood or air? How could you test these hypotheses? Do dragonflies sting their prey?
#23
4:29 to 4:44 / ECU to CU / Extreme close-up of the lower thorax at the point of wing bud attachment switches to a CU from the side with abdomen extending. / Is there any relationship between dragonfly length and weight or between either of these and final wing length?
#24
4:44 to 5:01 / FS to CU to ECU / Sideview of the entire body with abdomen and wings appearing to ‘pulse.’ In the ECU of the wings, veins in the wing are readily seen. Parts of the wings don’t look expanded and resemble crinkled cellophane. / Is this a male or a female? Could we tell if this is a female or a male at this point? What physical traits are used to identify dragonfly species? How do the wings complete their development?
#25
5:01 to 5:08 / FS / Sideview of the entire body / How long does it take for the dragonfly to be able to fly? What speed do they fly at compared to honey bees or birds? Do dragonflies with longer wings fly faster? What factors determine how fast an insect flies?
#26
5:08 to 5:26 / FS / Dragonfly on a bulrush. Wings which were together on its back are now extending horizontally. Wings obviously beating independently. / Do maturing dragonflies change colour? How accurate are their various senses and which are most important?