Some time ago, James Cheshire asked whether cowries really can emit
sulfuric acid, as reported. I don't know, but sulfuric acid, a very
corrosive substance, is not unknown in nature as a defense. In "Marine
Algae of California" (Stanford University Press, Stanford, California,
1976, p. 220), I. A. Abbott and G. J. Hollenberg state that the seaweed
Desmarestia is "remarkable in the field owing to large amounts of acids
produced when plants are collected, bleaching nearby plants and producing
an acrid odor." I have elsewhere seen it suggested that sulfuric acid is in
this mix.

It would be very remarkable if any shelled mollusk used any acid as a
defense, considering the harm that might occur to the shell, but nature is
remarkably inventive. Does anyone know of any examples?

Andrew K. Rindsberg
Geological Survey of Alabama