MAY
2011

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

Download the audio files or subscribe to our podcast.

 

 

 

 

05-26-11

Download the audio of On Six Legs: MP3, WMV.

The Sounds of Insects


bumble bee in flight
Bumble bee in flight

You may not have heard about it, but in spring 2000, the World Forum for Acoustic Ecology - WFAE for the acronym users among us - introduced a new scientific journal. It's called "Soundscape: The Journal of Acoustic Ecology." This Australia-based organization and journal, as you might have guessed, is devoted to sounds in nature.

Canadian R. Murray Schafer coined the term soundscape. According to Schafer, a composer and environmentalist, the soundscape consists of three components.

First are keynote sounds. These are sounds present on a regular basis, the background sounds. Depending on the location keynote sounds could be anything: lapping of ocean waves, wind in pine or willow trees, vehicle traffic on city streets, cattle grazing in a pasture, or the hum of a home air-conditioning system.

The second types of sounds are called signals. Things like bells, whistles, horns, a barking dog or crowing rooster. Signals stand out from the background sounds.

The third type of sound is defined as a soundmark. Soundmarks are like landmarks in that they can be used to define an area. I suppose the ringing of Big Ben, the bell in the Palace of Westminster in London, would be such a sound.

green cricket on a tree with wings up
Snowy tree cricket singing

Some insects produce sound and, as a result, can contribute to the soundscape. Insects create sounds by rubbing one body part against another, by vibrating their wings or by forcing air from spiracles.

Sometimes the insect sounds are incidental, produced by activities such as flying or chewing. Many times an insect deliberately produces sound in order to attract a mate, define territory or frighten a predator. Regardless of the reason the sounds of insects are a part of the soundscape.

Many insect sounds are included in the soundscape. Keynoters among the insects would be crickets, katydids and grasshoppers. These are stridulators - insects that rub one body part against another, such as a wing on a leg, to produce sound. The insect stridulators generate the clicks, scrapes and trills that are the insect contribution to the summer and fall soundscapes. In general, the human population ignores these insect sounds.

However, there are some insect sounds that do get our attention. These are sounds associated with stinging or biting insects. In this case it is the sound produced by the vibration of the wings. Based on soundscape terminology, insect sounds such as these would be called signals. Warning signals! That is exactly how stinging insects want the system to work. Their sound alerts humans to the fact that the insects are dangerous and should be avoided. Animals other than humans also learn to associate wing-beat frequency with the possibility of an unpleasant encounter with a stinging insect.

So effective is this insect-sound signal that even an insect that poses no harm to man or animal benefits from it. For instance, the green Junebug has a wing-beat frequency similar to bumble bees, and the sound they produce sometimes freaks people out, even though the green hard-shelled insect does not look anything like a bumble bee.

The frequency of the wing beat of mosquitoes produces a high-pitched whine that most of us recognize as an ominous sign that a female mosquito is seeking a blood meal. Because most of us don't think highly of the possibility of donating blood to a pregnant mosquito, the sound is a signal. A signal that indicates it's time to go inside or get out the insect repellent.

Periodical cicada on green leaf
Periodical cicada

Similar to a landmark, a soundmark would unique to an area. To me, the one type of insect sound that might come close to qualifying as a soundmark would be the sound of periodical cicadas. Cicadas are the drummers of the insect world and produce an incessant vibrating sound that in terms of decibel levels is unrivaled in the insect world. Because periodical cicadas are found only in parts of North America, their emergence every 17 years and the resulting singing could be considered a soundmark.

The sounds of insects, like the creatures themselves, can produce positive or negative responses from people. Some people like the humming of bees around flowers. To other folks the sound of a bee means trouble is brewing. As it turns out, insect sounds are not much different than other sounds in the soundscape. Some people like them; some people don't.

 

 

Writer: Tom Turpin
Editor: Olivia Maddox