In adults, the tympanum is covered and protected by the wings, and allows the grasshopper to hear the songs of its fellow grasshoppers. The grasshopper tympanum is adapted to vibrate in response to signals that are important to the grasshopper. Male grasshoppers use sounds to call for mates and to claim territory. Females can hear the sound that males make and judge the relative size of the male from the pitch of the call large males make deeper sounds.
Other males can hear the sounds and judge the size of a potential rival. Males use this information to avoid fights with larger male grasshoppers or to chase smaller rivals from their territory. Tags: Science Technology. Facebook Twitter. These ancestral insects went on to diversify into more than , species, and while most remain as deaf as their ancestors, some gained the means to hear. Of the 30 major insect orders, nine at last count include some that hear, and hearing has evolved more than once in some orders—at least six times among butterflies and moths.
The , species of that most dazzlingly diverse group, the beetles, are almost all deaf, yet the few that have ears acquired them through two separate lines of evolution. All told, insect ears arose more than 20 separate times, a sure-fire recipe for variety.
Among moths and butterflies, ears crop up practically anywhere, even on mouthparts. The bladder grasshopper has an abundance of ears with six pairs along the sides of its abdomen. Those detectors occur throughout the insect body but evolution typically only modified a single pair—apparently, almost any pair—to perceive the airborne vibrations generated by sound. From there on, each new attempt to forge ears went even further in its own direction as other structures were co-opted and reconfigured to capture, amplify and filter sound, extract the relevant information and convey it to the nervous system.
In mosquitoes and fruit flies, sound causes fine antennal hairs to quiver. Some eardrums are backed by air-filled acoustic chambers, others by fluid-filled ones. The number and arrangement of sensory cells that detect and decode those vibrations—and the neurons that send the signals to the brain—also vary from ear to ear. Some ears are relatively simple; others have extra bells and whistles linked to their lifestyle.
Take the parasitic fly Ormia ochracea , which deposits its larvae on a particular species of cricket after identifying and locating it from its characteristic call. Yet they take the prize for accurate location, thanks to an elastic band connecting the eardrums so they rock up and down like a seesaw, ensuring sound hits one ear fractionally later than the other.
The first is a small, hard plate behind the eardrums; the second, a fluid-filled tube containing a line of sensory cells. The signal then travels in a wave along the tube and over sensory cells tuned to different frequencies—making this organ a miniature, uncoiled version of our own, snail-shaped cochlea. The team has now gone on to show why female katydids are so good at finding a mate in the dark, even though their ears are close together not so close as those of the parasitic Ormia , but near enough to make pinpointing sound a sizeable challenge.
Our own ears lie on either side of our large heads and are far enough apart for a sound to reach them at different-enough times and loudness for the brain to compute and locate the source.
Katydids solved the problem again, in a unique way by enlarging a breathing tube that runs from a pore in the side of the chest to the knee; sound reaches the eardrums both from outside the body and from the inside via the tube.
If how insects hear varies enormously, so does what they hear. Mosquito ears are good for maybe a meter; the many-eared bladder grasshopper can hear from a kilometer or more away. Cricket ears detect low frequencies; mantis and moth ears are tuned to ultrasound, way beyond anything humans or their dogs can hear.
But what drove evolution to turn stretch receptors into ears in the first place, and so bring sound to the insect world? In modern insects, one of the primary functions of ears is to hear the approach of a predator in time to take action and avoid it.
The insects then respond with characteristic moves to escape the sonar beam: sharp turns, loop-the loops, air-to-ground power dives. Certain tiger moths even jam the bat sonar with clicks of their own. If predation is a powerful driver of evolution, so, too, is sex. And sound is an efficient way for an insect to identify itself to prospective mates: Sound travels well, works in the dark and provides the means to develop signature songs and private communications that no one else can hear.
In some cases, researchers are reasonably sure. Cicadas seem to have evolved hearing for mating purposes: Only singing species have ears and they are sensitive only to their own low-pitched songs.
For moths, bats were the trigger. Lepidoptera have been around some million years, yet no moths had ears before echolocating bats arrived on the scene about 60 million years ago. And many of the eared moths are sensitive only to the frequencies employed by their local bats—strong evidence that the ears evolved as bat detectors.
In adults, the tympanum is covered and protected by the wings. The tympanum has characteristics that are similar to a drum. Beating on a drum with a mallet will vibrate the drum head membrane to create a sound.
Drum heads can also respond to sounds. When sound waves of the correct frequency and amplitude hit the drum head, the drum will vibrate. Good drummers know this. If you watch the drummers in an orchestra, you will see that in quiet passages where the drums are silent, the drummers will place a finger or hand on the drum head to dampen the vibration and keep the drum quiet.
The grasshopper tympanum is adapted to vibrate in response to signals that are important to the grasshopper.
Male grasshoppers use sounds to call for mates and to claim territory. Females can hear the sound that males make and judge the relative size of the male from the pitch of the call large males have make deeper sounds. Other males can hear the sounds and judge the size of a potential rival. Males use this information to avoid fights with larger male grasshoppers or to chase smaller rivals from their territory.
The large white membrane on the abdomen of this grasshopper is its sound detection organ, the tympanum. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account.
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