THE BIOLOGY OF THE MUD-DAUBING WASPS 53 



I assume that each nest is built and filled by only one mother, 

 and in this assumption I feel fairly confident. So when we 

 find all of the young of one mother (as in some nests we do), 

 either emerging as adults or dying in the stage just preceding 

 emergence, then I say this mother has endowed her offspring 

 with better constitution to do battle with adversities during 

 its postembryonic development than the mother whose entire 

 progeny has died in early larvahood. 20 



The greatest elimination occurred in the prepupal stage. Of 

 course we must bear in mind that in the winter brood this stage 

 covers a long period when, the organism rests in this condition 

 during the winter, not transforming into a pupa until early 

 spring; hence we must expect a proportionately greater mortal- 

 ity. In some cases we find whole families dying in this stage 

 of their development; in other colonies the individuals live 

 through this critical period only to drop off later, for reasons 

 unexplained, and still others all survive to adulthood. In some 

 cases they never reach even full growth in the larval stage. 

 But the point that we would emphasize Here is that the young 

 not only die, but a certain considerable proportion of them die 

 with precision and system. When we find all of the population 

 of a nest arriving at an advanced stage, or in another all dying 

 at an early stage of their development, are we not right in sus- 

 pecting that the good tendency or the bad tendency "runs in 

 the family" or may be heritable? 



In going into a study of elimination in this group, we should 

 bear in mind that the mud-daubing wasps offer us material 

 which is peculiarly simplified for such a study. Many species 

 during their development from egg to adult would have to face 

 the chance of elimination in open competition with their fellow- 

 beings and enemies, and can only reach adulthood by surviving 

 climatic conditions in the open and also by exercising enough 

 energy and art to procure their own food during tender youth 

 as well as avoiding being food for others. But with these wasps 

 the case is very different. Not an iota of exertion or responsi- 

 bility is required of them until they arrive at adulthood. In 

 this part of the population, where the young are constantly 



20 Variable environment can scarcely have been a factor here, since all of the 

 nests here considered were taken from the rafters of the same barn, in equally 

 sheltered positions. 



