34 PHIL RAU AND NELLIE RAU 



While I can agree with Mr. Ashmead in regard to obtaining 

 adults of T. clavatum from the nests of Pelopoeus or Chalybion, 

 I cannot agree to the statement of both himself and Mr. Walsh 

 that T. albitarsis uses the old cells of both these species. Many 

 hundreds of adults have emerged from pipe-organ cells in my 

 possession. In addition I have invariably seen these wasps at 

 work on these nests, so I can hardly think of them as using 

 old cells of other wasps. 



One often finds nests parts of which, and especially the middle 

 parts, are two, three or even four tiers high, one built on top 

 of the other, as shown in fig. 1, where two layers exist and a 

 third is being commenced. Whether one mother constructs tier 

 upon tier, or whether a second mother builds her nest on top 

 of the first I do not know. This condition occurs almost too 

 frequently to be attributed to mere accident. Nevertheless the 

 occurrence of nests in this form brings out an interesting point 

 in the instinct of the emerging wasp. 



Fabre 7 carried on some experiments with the mason-bee 

 Chalicodoma muraria, in which he found that instinctively the 

 animal could bore out of only one earthen covering, and while 

 apparently it had the physical ability to emerge from an extra 

 covering it would rather die in its prison-house than make the 

 extra exertion to escape. But how fares it with these wasps 

 whose mothers or aunts build tier upon tier, making it necessary 

 for the emerging wasp to bite through more than one wall before 

 gaining its freedom ? It is interesting here to note that the 

 insects seem to have some faculty of discerning the front side 

 of their cells, just as the larva of the blue wasp or the yellow- 

 legs has the faculty of righting itself about in its cell as it reaches 

 maturity so that it always pupates with its head toward the 

 exit. In T. albitarsis nests of only one layer of cells, one seldom 

 sees an error in choosing the proper side for exit. It has been 

 my good fortune to obtain a few nests which were two or more 

 layers deep, and to study their contents to learn whether these 

 wasps did plod faithfully on until they gained their freedom, 

 or gave up at the first defeat. I have little doubt that there is 

 sufficient strength in those mandibles to penetrate several walls, 

 so the question is merely one of instinct. One nest of two 

 layers was placed flat upon a table so that the emerging insects 



7 The Mason-Bees. Tr. by A. T. De Mattos. Chap. II. 



