Bug-Eyed: What Kind of Eyes do Grasshoppers Have?

Problem

What kind of eyes do grasshoppers have?

Materials

• grasshopper (Catch it by following the instructions below or purchase one from a catalog supplier. See the Appendix.)
• insect net from Chapter 1
• 1-quart (1-liter) jar
• knee-high stocking
• magnifying lens

Procedure

CAUTION: Grasshoppers may bite, so do not hold one with your bare hands.

1. Catch a grasshopper by sweeping the insect net through high grass.
2. Transfer the grasshopper to the jar and cover the jar's mouth with the stocking.
3. Use the magnifying lens to study the head of the grasshopper, looking specifically for the eyes shown in the diagram.

Results

The grasshopper has two large eyes, one on each side of its head. It has three small eyes that look like little bumps between the two large eyes.

Why?

The grasshopper, like most adult insects, has two large eyes called compound eyes, one on each side of its head. These eyes are made up of thousands of separate units called ommatidia. At the surface of each ommatidium is a lens called a facet (A lens is the part of the eye that focuses light rays.) The ommatidia are grouped together so that the facets form a honeycomb pattern. Each ommatidium receives a small bit of light from the total scene that the insect sees. These separate images are sent to the brain, where they are combined to form the whole picture.

Many adult insects also have smaller eyes called ocelli, or simple eyes. The grasshopper has three simple eyes, all located between its compound eyes. Simple eyes do not have ommatidia and have only one facet. They can see the difference between light and dark, but cannot see images.

Let's Explore

Are the locations of the compound and simple eyes the same for all adult insects? Repeat the experiment, studying the eyes of other insects, such as crickets or prayingg mantises. You can safely catch these insects with your hands. Crickets can also be purchased at pet stores. Science Fair Hint: Make diagrams for a display showing the position and size of the eyes of different insects.

Show Time!

1. Scientists do not know what an insect actually sees. To get an idea of what it might be like to receive images from the multiple facets of a compound eye cut a toilet-tissue tube so that it opens: Stand 24 flexible drinking straws together on a flat surface, flexible sections up. Wrap the toilet-tissue tube around the flexible parts of the straws. Secure the tube with tape.

Hold the free end of the tube near, but not touching, your eye. Close one eye and look through the tube with your open eye. Look at stationary and moving objects, such as the blades of a rotating ceiling fan. Display the eye model along with diagrams of compound eyes and ommatidia found in insect books, such as Insect by Lawrence Mound (New York: Eyewitness Books, Dorling Kindersley /Knopf, 1990, pages 14–15).





2. Some insects can distinguish colors. Determine whether insects are more attracted to certain colors. Make a sugar-water solution by mixing 1 tablespoon (15 ml) of table sugar with 1 cup (250 ml) of tap water. This will attract insects that feed on nectar (a sugary liquid produced by many flowers at the base of their petals). Fill small, equal-size bowls or jar lids half full with the sugar-water solution.

Cut 6-inch (15-cm) circles from differently colored poster board, such as yellow, orange, red, blue, green, and black. Set these circles on a table or on the ground outdoors. Evenly distribute the circles and leave about 4 to 6 inches (10 to 15 cm) of space between them. Place one sugar-water container on each circle. Stand at a distance of about 10 feet (3 m) and use binoculars to observe the containers periodically for at least 30 minutes. Make note of the number of insects visiting each container. Make observations as often as possible every day for 3 to 4 days. Replace the sugar water each day. Use insect field guides to identify the insects visiting the containers.

Check It Out!

Insects cannot move or focus any of their eyes. How does the position of the compound eyes affect the direction that insects can see? Are insects nearsighted or farsighted? Do they have binocular vision?

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From this Book:

Janice VanCleave's Insects and Spiders
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