144 
Psyche 
[December 
season. The indications are that in the course of 11 evolu- 
tion, P. rubiginosis is becoming, in nest-building habits, 
more like Vespa crabro than it is like any other species of 
Vespa or Polistes, because they build in dark and inacces- 
sible places, and build comb beneath comb. 
A nest was taken at Wickes on September 7, 1919. Two 
days later, I noticed that one capped cell had an incision, 
and further observation showed a parasite in the act of 
emerging. The cap was removed, and under it I found the 
shrivelled pupa of P. rubiginosis pushed up toward the 
capped opening, and one-third of the distance down in the 
cell was a second cap or partition. This proved to be the 
covering of a series of elongated cocoons, each containing 
Fig. 6. 
a parasite, Christelia arvalis Cress. [R. A. Cushman], (fig. 
6). In this particular case the host, despite parasitization, 
had succeeded in spinning its cap, but in four other cells in 
this nest infestation had occurred earlier, so the wasp 
larvae had not the strength to spin their own coverings. 
Each parasite had spun its own cocoon; some had spun in 
nearly a horizontal position, others had spun in an upright 
position against the wall. The Polistes cells each contained 
about six cocoons of the parasite. 
11 When rubiginosis has sufficient room to build, the nests are very 
evenly made, and beautifully hexagonal in shape. When the condi- 
tions are crowded and space limited, the nests are made in various 
shapes, as shown in the collection of six in fig. 4. In fig. 3, which 
is another view of fig. 2, one can see more of the ill-shaped handiwork. 
IJowever, if one looks closely in the center of the lowermost nest in 
the latter figure, one can see how the nest started out to be hexagonal, 
but the additions added to either side grew according to the available 
space. 
