42 PHIL RAU AND NELLIE RAU 



economy however, since that room could have been used nicely 

 for another babe. This condition was seen so often that it 

 cannot be attributed to the whim of an occasional individual. 

 In one case we found a living 5. caementarium prepupa pushed 

 away back and entombed. The mother caementarium had failed 

 to seal her cell after laying the egg, and the little clavatum treated 

 it as she usually treats rubbish. 



In a collection of about a dozen mud-dauber's nests taken 

 in the spring of 1909, one nest gave forth six individuals of 

 Trypoxylon cockerellae Rohwer, identified by Mr. Rohwer. 



Another member of this group of house-renters is Pseudagenia 

 adjuncta Banks. (Identified by Mr. S. A. Rohwer.) This wasp 

 makes complete new cells inside the old cells of mud-daubers' 

 nests (see figs. 20, 23 and 26), and also makes complete cells 

 in the old empty cocoons of T. albitarsis (fig. 21). These insects 

 emerged from material gathered at several places near St. Louis, 

 and the adults emerged in late April and early May. I have 

 not observed the insect in the larval stage, but their pupal 

 covering is very thin and papery and of a cream white color. 



Likewise a sister species, Pseudagenia mellipes Say, 16 shares 

 the benefits of the mud nests. They do not make pretty little 

 cells inside the old mud-daubers' cells, as does P. adjuncta, but 

 they emerge from the outside walls of the nest, and I suspect 

 that their nidification occurs in this way. A mother finds the 

 nest of a mud-dauber and with her mandibles digs a small 

 cavity in the outer wall; this she fills with provisions and the 

 egg. Then with the mandibles she removes more earth from 

 the nest and builds up and around her mass until it is com- 

 pletely hidden. If the Sceliphron is at work at the time, so that 

 P. mellipes can get the wet mud, the work is greatly facilitated. 

 Fig. 22 illustrates the mud-daubers' nests with a portion of the 

 top removed to show the cells from which P. mellipes emerged. 

 It may be possible that P. mellipes does not dig out her supply 

 of mud from the nest, for in that event she would be obliged to 

 moisten it in some way. But if she brings it from afar I cannot 

 account for the mandible marks which usually are in evidence 

 near by. This species makes a pupal case of soft, white material 

 which is identical with that made by P. adjuncta. It appears 

 that these little builders may often be aided in their work by 



16 Also identified by Mr. S. A. Rohwer. 



