66 SOCIAL LIFE IN THE INSECT WORLD 



incontestably nourish them is quite another matter. The 

 disturbance of the soil warns the larva of danger. It 

 withdraws its proboscis in order to retreat along its 

 galleries, and when the spade uncovers it has ceased 

 to feed. 



If the hazards of field-work, with its inevitable dis- 

 turbance of the larvae, cannot teach us anything of their 

 subterranean habits, we can at least learn something of 

 the duration of the larval stage. Some obliging farmers, 

 who were making some deep excavations in March, were 

 good enough to collect for me all the larvae, large and 

 small, unearthed in the course of their labour. The 

 total collection amounted to several hundreds. They 

 were divided, by very clearly marked differences of size, 

 into three categories : the large larvae, with rudiments of 

 wings, such as those larvae caught upon leaving the earth 

 possess ; the medium-sized, and the small. Each of 

 these stages must correspond to a different age. To 

 these we may add the larvae produced by the last hatch- 

 ing of eggs, creatures too minute to be noticed by my 

 rustic helpers, and we obtain four years as the probable 

 term of the larvae underground. 



The length of their aerial existence is more easily 

 computed. I hear the first Cigales about the summer 

 solstice. A month later the orchestra has attained its 

 full power. A very few late singers execute their feeble 

 solos until the middle of September. This is the end of 

 the concert. As all the larvae do not issue from the 

 ground at the same time, it is evident that the singers of 

 September are not contemporary with those that began 

 to sing at the solstice. Taking the average between these 

 two dates, we get five weeks as the probable duration 

 of the Cigales' life on earth. 



