298 SOCIAL LIFE IN THE INSECT WORLD 



I see the tiny grub perforate the horny skin that covers 

 the cotyledons ; I watch its efforts ; I surprise it sunk 

 half-way in the commencement of a burrow, at the 

 mouth of which is a white floury powder, the waste 

 from the mandibles. It works its way inward and buries 

 itself in the heart of the seed. It will emerge in the adult 

 form in the course of about live weeks, so rapid is its 

 evolution. 



This hasty development allows of several generations 

 in the year. I have recorded four. On the other hand, 

 one isolated couple has furnished me with a family of 

 eighty. Consider only the half of this number — sup- 

 posing the sexes to be equal in number — and at the 

 end of a year the couples issued from this original pair 

 would be represented by the fortieth power of forty ; in 

 larvae they would represent the frightful total of more 

 than five millions. What a mountain of haricots would 

 be ravaged by such a legion ! 



The industry of the larvae reminds us at every point 

 what we have learned from the Bruchus pisi. Each grub 

 excavates a lodging in the mass of the bean, respecting 

 the epidermis, and preparing a circular trap-door which 

 the adult can easily open with a push at the moment of 

 emergence. At the termination of the larval phase the 

 lodgements are betrayed on the surface of the bean by so 

 many shadowy circles. Finally the lid falls, the insect 

 leaves its cell, and the haricot remains pierced by as 

 many holes as it has nourished grubs. 



Extremely frugal, satisfied with a little farinaceous 

 powder, the adults seem by no means anxious to aban- 

 don the native heap or bin so long as there are beans 

 untouched. They mate in the interstices of the heap ; 



