112 THE CAUSES WHICH PROPAGATE 



passing off; and, further, that it has yet to be determined 

 whether the several species, viewed in regard to sex and stage 

 of development, present gradations in their capability for music, 

 or not. 



STRIDULATION OF THE LEPIDOPTERA. 



Let us now repair to the fragrant orange-groves of the 

 New World, and listen to the rattling of love- wounded 

 butterflies that there meet, to chase through noon-tide twilight. 

 " The large and brilliantly-coloured Lepidoptera of Brazil,^'' says 

 Dr. Darwin, "bespeak the zone they inhabit far more plainly than 

 any other race of animals ; I allude only to the butterflies, for 

 the moths, contrary to what might have been expected from 

 the rankness of the vegetation, certainly appeared in much 

 fewer numbers than in our own temperate regions. I was 

 much surprised at the habits of Ageronia feronia. This but- 

 terfly is not uncommon, and generally frequents the orange- 

 groves. Although a high flier, yet it very frequently alights 

 on the trunks of trees, on these occasions its head, invariably 

 placed downwards, and its wings are expanded in a horizontal 

 plane, instead of being folded vertically, as is commonly the 

 case. This is the only butterfly which I have ever seen that 

 uses its legs for running. Not being aware of this fact, the 

 insect more than once, as I cautiously approached with my 

 forceps, shuflled on one side just as the instrument was on the 

 point of closing, and thus escaj^ed. But a far more singular 

 fact is the power which this species possesses of making a 

 noise. Several times when a pair, probably male and female, 

 were chasing each other in an irregular course, they passed 

 within a few yards of me, and I distinctly heard a clicking 

 noise, similar to that produced by a toothed wheel passing under 

 a spring catch. The noise was continued at short intervals, 

 and could be distinguished at about twenty yards distance.''^ 



Darwin is corroborated by Mr. A. R. Wallace. " This, the 

 common Ageronia (at Para), produces it remarkably loud, when 

 two insects are chasing each other, and constantly striking 

 together. One alone does not produce the sound in flying, 

 and I have never heard it made by the small species A. CJiloe, 

 which is equally common with the other. I am inclined, there- 

 forCj to believe that it is produced in some w^ay by the contact 



