Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
SAF Archives  search ask the scientists in the classroom cool science
Guide Index

The Eternal Wing

Taking to the Air

Cockpit Confusion

Bird Man

Roboflyers

Viewer Challenge
in the classroom
TEACHING GUIDES


FLYING HIGH: Taking to the Air


Just how insects evolved wings and learned to fly has long puzzled scientists. Dr. James Marden, a Pennsylvania State University biologist, has a theory that may explain how insect wings developed and provide an answer to the question, "What good is the nub of a wing?" Marden's inquiries take him into the Pennsylvania woods in late winter, where he and his students gather winter stoneflies. Before going to Pennsylvania, meet some aerobatic dragonflies captured on slow-motion video.

Curriculum Links
Activity 1: Modeling Insect Wings
Activity 2: Math Connection




CURRICULUM LINKS


BIOLOGY

anatomy,
arthropods,
invertebrates
GENERAL SCIENCE

insects,
natural selection
LIFE SCIENCE

evolution

MATH

quantifying surface tension
PHYSICAL SCIENCE

surface tension





ACTIVITY 1: MODELING INSECT WINGS

As you see on FRONTIERS, the wings of flying insects may have developed from smaller wing-like extensions that aided the organism in sailing or skimming across the water's surface. In this activity, you will construct insect models that illustrate the action of these adaptations and the properties of surface tension.

Materials:

  • plastic foam packaging "noodles"
  • toothpicks
  • clay
  • aluminum foil
  • paper
  • small tubs or large cookie trays
  • washers
Objective:

Operationally define skimming and surface tension.

Procedure:

  1. Working in groups of two or more, build a model of a stonefly using a plastic foam "noodle" or "peanut" to represent the insect's body.

  2. Break three toothpicks in half; each half represents an insect's leg.

  3. Cut six squares of aluminum foil, 1/2" on each side.

  4. Place a small lump of clay in the middle of each of the six foil pieces.

  5. Insert one end of each toothpick into the clay. Insert the other end into the plastic foam noodle.

  6. Construct a second model following the steps above. Add a paper sail to this model (try different positions and shapes for the sail to see which is most effective).

  7. Fill a large cookie tray with water about 1/4" deep.

  8. Blow through a straw and race the models across the cookie tray.

  9. After the race is finished, compare the actions of the two different designs. How does the sail-like wing give the insect an advantage? Experiment with different sizes and shapes of wings, and then design and test a more efficient sail. When you are satisfied with your design, enter it in a classroom race challenge.
Questions:

  1. Do you think your stonefly model would have been supported by the water's surface tension without the aluminum foil pieces?

  2. Was the most efficient sail design the largest?

  3. How might the stonefly adjust its path?
Answers:

  1. No; without the foil there is too little surface area to support the model.

  2. No; larger sails make the model unstable.

  3. Change the position of its body and wings.




ACTIVITY 2: MATH CONNECTION

Surface tension -- the skin-like cover of a liquid produced by the cohesion of its polar molecules -- allows tiny insects to walk on top of water without sinking. To calculate the relative force that can be supported per unit of water surface, modify your insect model by adding an extra toothpick and aluminum washers.

Procedure:

  1. Determine the total surface area of one leg pad.

  2. Determine the total surface area of all six pads.

  3. Add a toothpick to the middle of the model's back. Then measure and record the mass of the model.

  4. Measure and record the mass of one washer.

  5. Place the model on top of the water. Carefully add a washer by sliding it over the toothpick. Add washers until the model's weight can no longer be supported by surface tension.

  6. When the model sinks, calculate its total mass prior to the placement of the last washer (model plus washer weights). Divide this value by the total surface area to determine the force/unit area supported by surface tension.





 

Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.