156 WASPS [CH. V 



the fly upon the outer wrappings of the nest and may 

 often be seen as small white specks upon the surface. 

 When the grubs hatch they fall to the bottom of the 

 cavity and bury themselves in the loose soil, damp with 

 the matter that falls upon it. I have however seen the 

 eggs deposited direct upon the mass of filth below the 

 nest. In this case the nest was of V. sylvestris and had 

 been built in a library book-case, being suspended from 

 a shelf. The excreta were consequently fully exposed 

 upon the top of the shelf next below. The grubs of 

 Volucella inanis have been seen by Janet moving about 

 the combs and visiting cell after cell, apparently de- 

 vouring the excreta of the wasp larvae and doing no 

 injury to the occupants. It is remarkable that the adult 

 fly V. inanis very closely mimics wasps in its coloration. 

 It has been suggested that this resemblance enables the 

 fly to enter the nest unobserved by the wasps themselves. 

 In this connexion it is worth remembering that within 

 the nest there is very little if any light and that colour 

 can be of little, if any, value under such circumstances. 

 Marchal's explanation of the immunity of Volucella 

 zonaria, another mimic of like habits, is more probably 

 correct. He observed that the fly moved about within 

 the nest quietly and without excitement and thus avoided 

 attracting attention. On the other hand a strange wasp 

 introduced from one nest into another was greatly agitated, 

 and in spite of similarity of appearance was speedily slain 

 and ejected by the lawful tenants. It is interesting t& 

 learn from Janet that a newly hatched wasp when taken 

 to another nest is not thus maltreated. 



