330 WASP STUDIES AFIELD 



emergence at approximately the same time in the following 

 spring; and yet we cannot see how even then they could 

 make their way out without often coming into disastrous 

 collision. This may account, in part, for the large number 

 of dead adults of this species more than of B. nubilipennis, 

 which we have dug out in the spring. We have never as- 

 certained whether these dead wasps are the young adults 

 which never found their way out to the light of day, or 

 wasps of the parent generation which may have died while 

 sleeping in their burrows or may have been entombed by 

 the mud of heavy rains. 



The variation in the periods of development mentioned 

 above may help to clear up this conflict of the emerging- 

 wasps, or again it may only add to the confusion. This 

 point was suggested to us by a certain burrow, an ex- 

 ceptional nest in this vicinity in that it had three cells (fig. 

 62). We dug it up just after the top cell had been closed. 

 One would logically expect to find the occupant of the 

 lowermost cell of the tier the largest, but we were surprised 

 to find the larva in the middle cell large, the bottom one 

 small and the uppermost still of course in the egg stage. 

 How this state of affairs could have come about remains a 

 mystery. 7 We wanted to follow up this development, but 

 the lowest larva died. However, when they arrived at the 

 stage of pupation, the middle or largest one spun its cocoon 

 only three days earlier than the smallest one (which was still 

 in the egg stage when we found it). Hence we may be- 

 lieve that the difference in the date of maturation of these 

 and the intermediate one would have been even less. 



Fabre finds that, in certain bees, one sex hatches earlier 

 than the other, and the mother can control the sex of the 



7 The fact that the foregoing table shows the incubation of the egg 

 to vary from 2 to 6 days may mean a correlation of the period to the 

 sex of the developing larva. 



