A WEEK WITH A MINING EUMENID. 155 



DESCRIPTION OF THE NESTS. 



Each nest consists of one to three, usually two, barrel-shaped 

 or sub-spherical cells for larvae and a small air chamber, the latter 

 being above the former. Thin partitions of clay separate the com- 

 partments from each other and a clay plug separates the whole 

 from the outer world (Fig. 6, B-D). In the cases observed by 

 me, when there were three cells, the upper was empty ; when 

 there were two cells, the upper was smaller than the lower. These 

 nests vary in length from one and a half to two and three fourths 

 inches. Each cell is about five eighths of an inch wide and the 

 entrance to the nest is about three eighths of an inch. The trans- 

 verse partitions are thin. Each wasp constructs a succession of 

 nests which are arranged close together. These facts were ascer- 

 tained by excavating twenty-five nests. 



The above description harmonizes perfectly with Rau's observa- 

 tions and with the majority of Isely's ; however, the latter author 

 found some nests with as many as seven cells. 



EXCAVATING THE NEST. 



The nest-building behavior of these wasps is fascinating. Pre- 

 liminary to digging, the wasp makes sweeping movements over 

 about forty square inches of surface. She moves about here and 

 there as though testing the ground. The purpose of this survey 

 I do not know ; it may be that it enables her to detect the spots 

 where other nests are located. This surmise is supported by the 

 fact that excavations demonstrate that the nests occur in small 

 groups. The nests of each group are separated from one another 

 by walls that are not very thick ; yet I have never discovered one 

 burrow running into another. 



The preliminary explorations over, the wasp makes a flight of 

 orientation and then flies to the near-by streamlet and takes a deep 

 drink of water. Returning to the spot selected, she moistens the 

 ground and, with her mandibles, removes several pellets of dirt and 

 conveys them, one by one, to a distance of from two inches to two 

 feet. She then goes for some more water and then returns to the 

 excavating (Fig. 3, a). This is repeated over and over again until 

 the lower cell has been completed and the next one partly finished. 



