FLY-CATCHING WASPS 93 



found a H. stirpicohis boring into the soft pith. It had 

 in this brief time made a hole one-sixth inch deep. An- 

 other was found still at work burrowing in the pith at so 

 late a date as October 25. 



One fine nest in an elderberry twig was found in Novem- 

 ber. The burrow in the pith chamber was thirteen inches 

 long and one-fourth inch in diameter. The gallery was 

 not at all points in the center of the stalk, but oscillated 

 from side to side. Perhaps the wasp in digging it out had 

 merely followed the line of least resistance and had chosen 

 the softest spots. The partitions were made of the soft pith 

 firmly packed together. The thickness of the partitions and 

 the length of the cells were variable, as the following table 

 shows : 



Partition. Cell. Partition. Cell. 



I fa inches fa inch fa inch l / 2 inch 



i inch l / 2 inch % inch fa inch 



y 2 inch y^ inch y* inch 



y inch fa inch 



The upper five inches of the tunnel was open and unused. 

 All the six cocoons in the cells rested with the heavy end 

 toward the bottom, leaving the thin, easily opened covering 

 on the top. We do not know, however, whether these wasps 

 habitually emerge by boring through the side of the twig, 

 or by struggling through the pith to gain the top exit. In 

 another series of cells in a twig eight inches long, the parti- 

 tions in the upper half were broken and crumbled, as if the 

 occupants of the nest might have escaped by that way. Of 

 course, if they emerge by the open, upper end of the stalk, 

 the priority of the lower inmates offers difficulties. These 

 nine adults emerged during our absence, from April 12 to 

 28. Another neat nest very similar to this is illustrated, 

 exact size, in fig. 23. This had fourteen cells and eleven 



