THE BIOLOGY OF THE MUD-DAUBING WASPS 51 



Mortality in the prepupal stage 



Those eggs which are deposited in late August and September 

 winter over as prepupae in the nest. In a comparatively short 

 time the larvae consume their food and grow to full size, and 

 long before cold weather sets in they have spun their cocoons 

 about themselves and there they remain inactive, not trans- 

 forming into pupae until spring (about May). In this condition 

 they pass through the coldest part of the winter, and a part of 

 the mortality among prepupae may be attributed to the cold. 



When the cells are opened and dead prepupae are found, 

 they are of two kinds, (a) those which are dead, but are yet 

 white in color, which shows that they have died more recently 

 than (b) those which are of a decayed-looking, brown color, 

 showing their death to have been more remote, and hence having 

 occurred earlier in the season, when they had not experienced 

 much cold. In this collection we found 415 belonging to class 

 a and 629 to class b. This shows that the mortality was greater 

 in the earlier and milder period than during the colder season. 

 Of course other external factors may have been responsible for 

 the life or death of the insects, such as the thickness of the mud 

 walls, etc. 



The mortality at this stage including both early and late 

 deaths was 1,044, or about one fourth of the cells. There may 

 have been some inherent weakness in whole families, but this 

 will be discussed under mortality in individual families. 



Mortality in the pupal stage 

 After the insects have survived the winter in the prepupal 

 stage they transform into pupae. Here in the more advanced 

 stage of the insect's life the mortality was comparatively small, 

 110 cells, or 2 per cent, of the total. But even this number is 

 large when one considers that the insect is past most of its 

 frailties and difficulties, feeding, spinning and transforming; why 

 should these have died for no apparent cause at this vigorous 

 stage? This subject too will be considered again in the probable 

 inherent weakness of certain families. 



Mortality in the adult stage before emergence 



Here we have a rather perplexing form of mortality. The 

 insects had transformed properly into adults, had wings, legs, 



