190 SOCIAL LIFE IN THE INSECT WORLD 



is absolutely mute, even to the most sensitive ear. Does 

 she perhaps emit vibrations of such delicacy or rapidity 

 that only the most sensitive microphone could appreciate 

 them ? The idea is barely possible ; but let us remember 

 that the visitors must have been warned at distances of 

 some thousands of yards. Under these conditions it is 

 useless to think of acoustics. 



Smell remains. Scent, better than any other impres- 

 sion in the domain of our senses, would explain the 

 invasion of butterflies, and their difficulty at the very 

 last in immediately finding the object of their search. 

 Are there effluvia analogous to what we call odour: 

 effluvia of extreme subtlety, absolutely imperceptible to 

 us, yet capable of stimulating a sense-organ far more 

 sensitive than our own ? A simple experiment suggested 

 itself. I would mask these effluvia, stifle them under a 

 powerful, tenacious odour, which would take complete 

 possession of the sense-organ and neutralise the less 

 powerful impression. 



I began by sprinkling naphthaline in the room intended 

 for the reception of the males that evening. Beside the 

 female, inside the wire-gauze cover, I placed a large 

 capsule full of the same substance. When the hour of 

 the nocturnal visit arrived I had only to stand at the 

 door of the room to smell a smell as of a gas-works. 

 Well, my artifice failed. The butterflies arrived as usual, 

 entered the room, traversed its gas-laden atmosphere, 

 and made for the wire-gauze cover with the same 

 certainty as in a room full of fresh air. 



My confidence in the olfactory theory was shaken. 

 Moreover, I could not continue my experiments. On 

 the ninth day, exhausted by her fruitless period of 



