Field Studies of the Non-Social Wasps 429 
kneaded into shape by dextrous movements of the body; 
it then hardens and makes a very comfortable abode. 
These mud nests are usually built against some flat 
surface; sometimes the back side is lined with mud, and 
sometimes the board on which it is plastered serves as a 
back wall. Here in fig. 59, we have a view of the back 
of one such nest built without a mud wall, showing cells, 
partitions, pupal cases, spiders, empty cells and two cells 
in course of construction. In this nest are three in- 
stances of the emerging insect opening its way into an 
adjoining cell instead of to the outside; if the adult be- 
longing in the latter cell had already emerged, this wasp 
could leave by its exit, but if not it must certainly die 
imprisoned, because instinctively the insects can open 
their way through only one wall. 
In contrast to this flat form I have seen about a dozen 
nests built on hanging corn-husks. Here without a sub- 
stantial foundation the cells attained a perfectly cy- 
lindrical shape, as thick on the back as on the front. They 
afforded sufficient protection in all respects, however, for 
they brought forth healthy adults. Another nest was 
found attached to exposed roots under a bank (fig. 62). 
On two occasions I have been able closely to observe 
the details of the building operations of T. politum in 
progress. One nest that I was so fortunate to discover 
in course of construction was in an accessible position 
SO one could watch the methods of building. It contained 
two complete tiers and the third was being added. The 
wasp returned with a mouthful of mud, but our presence 
disturbed her and she few away. Only on her fourth re- 
turn was she content to settle down to her work without 
e tried to observe this process by placing organisms about 
to pupate is vials, but they were unable to work on smooth glass, and 
they produced only thick ribbons of the black material. 
