THE BIOLOGY OF THE MUD-DAUBING WASPS 49 



these unsealed cells, or about 3 per cent, of the total number. 

 Of these, 7 were partly filled with spiders. They occurred in 

 the following rate: 



96 126 



The table above shows that 96 mothers failed to seal their cells, 

 and while most of them (the 77 which failed in one case only) 

 might be attributed to some accident that prevented the mother 

 from returning, yet the 19 other cases prove that part of these 

 failures must be attributed to her carelessness. On two occa- 

 sions in my experience, adults emerged from these unsealed 

 cells of the summer brood. The closure therefore does not 

 affect the development of the larva, but it probably keeps out 

 parasites. 



Insufficient food in the cell 



Another occasional fault to be attributed to the forgetfulness 

 or carelessness of the mother wasp is that of laying the egg and 

 closing the cell with a supply of food that is quite insufficient 

 to bring her young to maturity. We find in some cases only 

 enough food to carry the larva through half its period of growth, 

 or even less. When the cells were opened up and dead larvae 

 found, it was noted whether any food remained uneaten in the 

 cell. If the larva was dead and part of the food was untouched, 

 its death was attributed to unknown causes. If however a 

 half-grown or stunted larva was found dead in the cell with 

 no food, its death was attributed to starvation, due to the 

 mother's failure to supply it with sufficient food. 



Only 46 cells, or 1 per cent, of all, were found in this condition, 

 and 35 mothers were responsible for this mischief; 29 of these 

 mothers had one such cell each in their nests, and these nests 

 were distributed among the large as well as the small nests 

 (2 to 26 cells). Four cases of two such cells in a nest were 

 among small nests. The mother that erred in this way three 

 times had a 7-celled nest, and last of all one wasp with a 25- 

 celled nest was woefully deficient six times. 



