In the early 1950s, there were newspaper reports that "research" had shown snakes to be completely deaf. This is incorrect. Although they have no external ear openings, snakes do have internal ears, and can hear some sounds although poorly. - Deaf-related Resources Gallaudet University Library Rattlesnakes and other snakes lack external ear openings, but snakes are not deaf. - South Dakota Div. of WildlifeSnake Bioacoustics: Toward a Richer Understanding of the Behavioral Ecology of Snakes
Bruce A. Young
Snakes are frequently described in both popular and technical literature as either deaf or able to perceive only groundborne vibrations. Physiological studies have shown that snakes are actually most sensitive to airborne vibrations. Snakes are able to detect both airborne and groundborne vibrations using their body surface (termed somatic hearing) as well as from their inner ears. The central auditory pathways for these two modes of "hearing" remain unknown. -
The Quarterly Review of Biology The Sensory Basis of the Honeybee's Dance Language; June 1994; Scientific American Magazine; by Kirchner, Towne; 7 Page(s)
For many centuries, naturalists have observed that honeybees tell their nestmates about discoveries they make beyond the hive. Nevertheless, the system of communication that the insects use remained a mystery until the 1940s, when Karl von Frisch of the University of Munich in Germany first discovered the significance of bees' dances. In the hive the steps and waggles of a successful forager correlate closely with the exact distance and direction from the nest to the resource she has discovered. For the next two decades, most scientists believed bees relied primarily on these silent movements to communicate.
In the 1960s this view was challenged in two ways. The first challengers were Adrian M. Wenner, then a graduate student at the University of Michigan, now at the University of California at Santa Barbara, and Harald E. Esch of the University of Munich, now at Notre Dame University. Working independently, the two researchers discovered that the dances were not silent after all. As the bees dance, they emit faint low-frequency sounds, and Wenner and Esch both suggested that the sounds might play a critical role in the bees' communication. The use of sounds, they reasoned, might account for the bees' ability to communicate effectively in the complete darkness that prevails inside their nests. At the time, however, many scientists believed bees were deaf, and so the issue remained open.
FREQUENCY RANGE of the sounds a bee can detect extends well below the range heard by human ears. The graph shows how fast the air particles near a dancer's wings must travel to generate audible signals. Within this range, the bees show an ability to differentiate between sounds having varying frequencies.
Bees, it turns out, can hear, and their ears are well suited for detecting the sounds associated with the dances. Observation of how the insects respond to a robot that dances and sings like a live forager shows that both sound and dance are needed to communicate information about the location of food. Silent dances, the experiment demonstrates, communicate nothing, and sound without dance also fails.
In our first series of experiments, we trained the bees to associate a sound, lasting for five seconds, with a very mild electric shock, arriving four seconds after the sound had started. We generated the sound at the open end of a narrow glass tube. The shock alone, if delivered while the bee was feeding, would drive the bee from the feeder for a few seconds; shortly thereafter she would return and continue feeding. We then posed the following question: If a bee repeatedly experiences a tone followed by an adverse stimulus, will she eventually learn to withdraw from the feeder within the first four seconds of the sound, before the shock? If so, then she can hear--and of course learn. We found that bees can indeed be trained to respond to airborne sounds, although they learned to do so very slowly.
More recently, we have employed a different training technique. In these experiments, a bee entered a very simple Y-shaped maze. We played a sound at one end of this two-sided feeder. The side from which the sound came changed unpredictably from one trial to next. If the bee turned toward the sound, she received a reward of sugar water; if she went away from the sound, she received nothing. We observed that the bees learned quickly to turn toward the sound. Claudia Dreller, a graduate student at Würzburg, used the procedure to explore the frequency and amplitude range in which the bees could hear. Dreller's work showed that honeybees sense only low frequencies, those below 500 hertz. They hear these tones with sufficient sensitivity to pick up the sounds of a dancing nestmate, which range from 250 to 300 hertz. They also show some ability to discriminate between frequencies in this range; they can discriminate between low- (20 hertz), medium- (100 hertz) and high-pitched (320 hertz) sounds.
We found that bees use a structure called the Johnston's organ, a chordotonal organ made up of nerve cells in the second joint of a bee's antennae, to pick up airborne sounds. Some fiies and mosquitoes rely on the same structure to perceive sounds.
The dancer emits sound signals that help the dance followers determine where the dancer is and how she is moving, which in turn offers them critical information regarding the direction and distance to the feeding site. The dance attenders receive these signals through the Johnston's organs located in their antennae, which are always held near the dancer. Because these organs are bilateral--one on the left and one on the right--the dance followers can use them to judge their position with respect to the dancer and therefore understand the direction to the food.
Although we have looked for dance sounds in four species of honeybees, we have found that only three produce them. These three species hold something else in common: they all must occasionally dance in the dark. Two of them, the familiar western bee, A. mellifera, and the Asian bee, A. cerana, nest in lightless, enclosed areas such as hollow trees or other similar cavities. The third sound producer, the giant bee, A. dorsata, nests in the open on single sheets of comb, hanging under rock outcrops or thick branches of trees. Fred C. Dyer of Michigan State University first showed that A. dorsata sometimes dances at night, and Kirchner discovered only recently that this bee produces sounds. A. dorsata's signals were very difficult to detect because these sounds are particularly low in pitch.
The single species that dances silently, the dwarf bee, A. fiorea, dances in the open like A. dorsata, but only during the day. -
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