In response to:
Queens of the Web from the May 1, 2008 issue
To the Editors:
In his review of David Attenborough’s Life in Cold Blood [NYR, May 1], Tim Flannery perpetuates a popular error that snakes are deaf to airborne sounds, and he misleads further by stating that their eyes are “of a rather defective structure.” Even by confining these claims to cobras, as he does for the sake of an argument, he is not on safe ground, since their hearing has not been tested adequately to my knowledge. Feeding rewards do not work with snakes, considering that they feed so rarely and then on large food items.
Neurophysiologists showed long ago that pine snakes, garter snakes, and water snakes can hear low-pitched, airborne sounds at frequencies of 100 to 700 cycles per second. In fact in the range of 100 to 200 cycles their ears are superior in sensitivity to those of a cat (E. G. Wever and J. A. Vernon, Journal of Auditory Research, Vol. 1 (1960), pp. 77–83). Some snakes surely are blind and probably deaf, such as a tiny worm snake in Nairobi living on termites and weighing as little as 125 mg as I determined.
On vision in general, G. Walls—whose lectures I attended at Berkeley—says in his classic The Vertebrate Eye (1942),
The snakes have rung as many changes upon visual patterns as have all other vertebrates put together. If anything could make a snake-hater learn respect and admiration for this abused group of animals, it would be the study of their eyes.
H.S. Robert Glaser
Professor, Department of Biology
Tim Flannery replies:
I’m grateful to Professor Robert Glaser for his insights into the sensory perceptions of snakes. My assertion that snakes are deaf can indeed be challenged if one defines hearing as the ability to detect vibrations transmitted through the ground or other solid substrates, or even very low frequency vibrations traveling through the air. This sensing of vibrations is achieved without ears.
My comment on the defective structure of snake eyes was prompted by Sir David Attenborough’s remark that “at some time in the distant evolutionary past, the eye [of snakes] became very degenerate and could only be redeveloped by elaborating its few surviving relics.” This Attenborough ascribes to snakes having gone through a largely subterranean burrowing stage during their evolution. No doubt some snakes have developed excellent sight using eyes that lack many of the features essential to good vision in other creatures.