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# Singers: How do Some Types of Insects Make Sounds?

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Source:
Author: Janice VanCleave

### Problem

How do some types of insects make sounds?

### Materials

• Index card
• Fingernail file or emery board

### Procedure

1. Hold the index card upright with one long edge resting on a table.
2. Support the card with one hand as you draw the rough side of the file across the top edge of the card quickly two times.
3. Wait one second and repeat steps 1 and 2. (You can measure 1 second of time by saying "one thousand one.")

### Results

You hear a rasping sound.

### Why?

Sounds are caused when materials vibrate (move back and forth). When you rub the file across the paper, the rough surface of the file plucks the paper's edge, causing it to vibrate. The vibrating paper produces sound.

Certain insects, like crickets and grasshoppers, produce sounds in much the same way. These insects make sounds by rubbing two body parts, usually one sharp-edged and the other rough or filelike, against each other. This process is called stridulation. The short-horned grasshopper or locust stridulates by rubbing its rough hind leg across the sharp edge of its wing. Most insect sounds are made by males to attract females and to warn other males away.

### Let's Explore

Most insect sounds do not get higher or lower, but remain constant throughout the sound. The sounds of related insect species are different because they have different rhythms (sounds in regular patterns). The length of time a sound is made and the time between sounds produces a rhythm. The rhythm in the experiment is the time between the sound produced by two quick strokes of the file across the card, silence for 1 second, then the sound of the two strokes again. Repeat the experiment, producing different rhythms. One way would be to first draw the file across the card very slowly two times. Then draw the file across the card quickly four to five times, followed by another second of silence before starting over.

### Show Time!

Demonstrate this method of sound production by cutting off the narrow part of a 12-inch (30-cm) round balloon. Stretch the bottom, rounded part of the balloon over the mouth of a 10-ounce (300-ml) plastic glass. Pinch the center of the stretched balloon between the thumb and index finger of one hand. Pull the pinched balloon outward, then release it.

1.
1. Some insects produce sounds by expelling (forcing out) air or liquid from some body opening. Insects usually produce these sounds in response to disturbances. Some cockroaches produce a hissing sound by expelling air from certain spiracles (breathing holes) in their bodies. Demonstrate this type of sound production by holding your teeth together and blowing air between them.
2. The death's-head sphinx moth produces a whistling sound as it expels air from its pharynx (throat). Use a balloon to show how expelling air can cause a whistling sound. Blow up the balloon and hold the open end with the index finger and thumb of both hands. Stretch the neck of the balloon outward to form a narrow opening and let the air out slowly.
2. Male cicadas produce very loud sounds by vibrating special membranes (thin, flexible sheets of tissue) called tymbals. The abdomen of the male cicada is almost completely hollow. The vibrating tymbals and the hollow abdomen act like a drum.
3. Insects also produce sound by vibrating their wings or other body parts. Bees and mosquitoes buzz because their wings vibrate. Use a vibrating index card to demonstrate the sound of an insect's vibrating wings. Stretch a rubber band around a 4-by-6-inch (10-by-15-cm) piece of cardboard. Place 2 pencils under the rubber band at opposite ends of the cardboard. Pluck the rubber band with your finger, then immediately touch the vibrating rubber band with the tip of an index card, which will make the index card vibrate. Use this and the other sound models to prepare a display for the different sound-producing mechanisms.
4. Create a display of each of the four methods of sound production described in this chapter: stridulating, expelling air, vibrating tymbals, and vibrating wings or other body parts. For each method, draw the model you made in each of the previous experiments along with a picture of an insect that uses that method to produce sound.

### Check It Out!

Organs for hearing, or "ears," are never found on an insect's head. Many insects hear by means of fine hairs on different parts of their body. Find out more about how insects hear. Can only adult insects hear sounds? Where are the hairs or hearing organs located on insects' bodies?