﻿flELL AND FOREST. 163 



how do the birds know the precise spots where their victims lie buried 

 in the sand ? That this knowedge is not derived by sight I am quite 

 sure, for I have repeatedly observed innumerable curlew marks of the 

 kind described occurring on tracts of sand which, in virtue of their 

 high level, presented a perfectly smooth and uniform surface. I can 

 therefore only suppose that the birds are guided in their probings by 

 their sense of hearing. Doubtless it is difficult to believe that this 

 sense is so delicate and precise as to enable the curlew to perceive so 

 exceedingly slight a sound as that which must be caused by the move- 

 ment, say of a small worm at a distance of ten or twelve inches from 

 the surface of the sand, and at the same time to localise the exact spot 

 beneath the surface from which so slight a sound proceeds. I cannot 

 see, however, that any other explanation is open, and perhaps the one 

 now offered may not seem so incredible if we remember the case of the 

 thrush. No one, I think, can observe this bird feeding and doubt 

 that it finds its worms and grubs almost exclusively by the sense of 

 hearing. And if the distance which it runs between successive pauses 

 for listening represents — as we cannot but suppose it must — the diam- 

 eter of the circle within which this bird is able to hear the movements 

 of a worm, I think that the hypothesis I have just advanced with re- 

 gard to the curlew ceases to be improbable. 



It seems worth while to add a few words with respect to the sense 

 of hearing in insects. So far as I am aware, the occurence of such a 

 sense in this class had never been actually proved, although on a priori 

 grounds there can scarcely be any doubt concerning the fact of some 

 insects being able to hear ; seeing that in so many species stridulation 

 and other sounds are made during the season of courtship. In the 

 case of moths, however, I believe that sounds are never emitted — ex- 

 cept of course the death's-head. It therefore becomes interesting to 

 observe that an auditory sense is certainly present in these insects. 

 Several kinds of moths have the habit of gently, though very rapidly, 

 vibrating their wings, while they themselves are at rest on a flower or 

 other surface. If, while this vibrating movement of the wings is going 

 on, the observer makes a sudden shrill note with a violin or fife, &c, 

 the vibrating movement immediately ceases, and sometimes the whole 

 body of the insect gives a sudden start. These marked indications of 

 hearing I found invariably to follow a note with a high pitch, but not 

 a note with a low one. 



