214 THE CAUSES WHICH PROPAGATE 



dance with j^eevish ring-, that some flies rise to the sunbeam with 

 a gay time^ and others meet in air with jealous cries, never- 

 theless, owing to the bluntness of human sense and slow process 

 of thought, the delicate modulations, as the purport of this 

 widely-spread music, as a rule elude our senses. But we are not 

 without proof that in those species w^here it assumes spontaneous- 

 ness, it is as capable as instrumental music of vindicating and 

 interpreting certain stimuli, as fear, love, and rivalry. 



The high spiracular note of the Syrphidce and yEolian murmur 

 of the 3Iuscida breaks forth in its varied compass when one is 

 held in the hand, or, driven by fate, falls into the meshes of the 

 autumnal spider hordes ; and species of Hover Fly thus greet 

 a predaceous insect as readily as a cat hails a dog. I remember 

 one morning when sauntering along the highland glen immor- 

 talised in " The Queen^s Wake,^'' catching a whinivg cry from 

 the sunny side of the road, and on proceeding to the spot 

 detecting an orange-belted fly wrestling on a buttercup-head with 

 a small Hymenoptera. Boxing them together under the net, 

 the fly crouched down at the bottom of the receptacle, con- 

 tinuing its distressful note, until its aggressor, after crawling 

 about for some seconds, darting down, seized it beneath and 

 decapitated it. 



A marked employment of this spiracular music in courtship 

 came under the notice of Col. Goureau. "^ On the 9th of July 

 I saw two Wasp Flies [Chrysotoxum arcMatum) sitting the one on 

 a fir branch, and the other on the leaf of a neighbouring beech. 

 Both were uttering a shrill and plaintive note. They flew away, 

 and returning, settled nearer to each other, and recommenced 

 their song. They repeated the manoeuvre again and again, at 

 times as they took wing, meeting in the air, and appearing to 

 seize each other, or falling precipitately towards the ground, 

 and as I watched them utter their eomj^laining cry, I noticed 

 a slight movement take place in the wings, which increased as 

 the sound gained in intensity, but ceased each time the insect 

 took flight, and was succeeded by the deej) hura.^^ 



We are here introduced to a species of dance accomjianying 

 the notes, and originating in the same stimuli, and no less do 

 spiracular murmurs of rivalry prompt aerial gambols. During 

 hot, cloudless July weathei-, there appears on the surface of wells 



