396 THE BUTTERFLIES OF NEW ENGLAND. 



these portions of the wing are rubbed together a noise is produced ; 

 while in other butterflies, such as Brenthis, not nearly so much contrast 

 appears. On examing these surfaces in the wing of a species of Agero- 

 nia in the Cambridge Museum, where I was kindly permitted to dissect 

 one specimen, these scales were found to have in addition a more or less 

 conical shape, as if to make the sound produced by their rubbing upon 

 their mates more intense, but of course it would be impossible to imitate 

 the " click" by any clumsy action of the hand. 



Many observers have noted the peculiar movements of the wings of 

 buttei-flies which are not accompanied by audible sounds, especially in the 

 family Lycaenidae, where the hinder wings alone, erect when the insect is 

 at rest, are rubbed together in a curious way, giving them " the appear- 

 ance of revolving disks," as Mr. Wallace calls it ; and many observers 

 have attempted to discover whether any sound followed this motion, but 

 none have succeeded in doing so. Yet any other explanation of the in- 

 tent of the movement would seem to be almost out of place, inasmuch as 

 it is invariably made by certain species, including many of our own native 

 kinds, directly upon alighting and at a time when there may well be no 

 other butterflies in sight.* Movements of some sort are made by a large 

 majority of butterflies ; as for instance in most of our Argynnidi and other 

 Nymphalinae, which gently wave their wings upward and downward upon 

 alighting, as if panting from their exertions. A marked instance of this 

 is seen in Vanessa atalanta. Still more striking instances are the quiver- 

 ing movements of the male settled beside the female ; or of a butterfly 

 eagerly sucking a flower when another alights beside it, and is thus warned 

 to " keep its distance." These motions I am inclined to regard as move- 

 ments for the sake of producing sound, though the sounds are inaudible to 

 our ears. It is probable that this is on account of their faintness. There is 

 a limit of human perceptibility of sounds from their shrillness and also from 

 their feebleness. It is known, but perhaps not well known, that there are 

 a certain number of saltatorial Orthoptera which can be seeyi to stridulate 

 but whose sounds are inaudible to our ears. (Compare Yersin on the 

 stridulation of Orthoptera, Bull. Soc. Vaud. sc. nat.) From the fact 

 that certain butterflies produce sound during certain movements, we can 

 hardly fail to believe that other butterflies making the same motion also 

 produce sound, although inaudible to our ears. 



Nor are the sounds made by these friends of ours altogether limited to 

 the butterfly state, a large number of caterpillars making sounds by 

 striking their heads against the leaf upon which they are resting, or by 

 swinging the head from side to side, catching the mandibles in the rough- 

 nesses of the leaf or upon the silken strands which they have spun upon it, 

 to produce a scraping sound to drive away intruders ; and Schild (Stett. 



*The mechanism of this presumable stridulation is discussed further on under the Lycaeninae. 



