438 Trans. Acad. Sci. of St. Louis 
found one nest infested by an Ichneumon fly belonging 
to the tribe Ophionini. Birds, also, while they are 
neither parasites nor inquilines, should be recorded as 
enemies of 7. politum, which cause heavy losses. It is 
a simple matter for a bird to peck through the mud walls 
of the pipe-organ nests, and we often find evidence of 
this injury. On one occasion a blue-jay was actually 
seen breaking into the nest and feasting upon the larve 
therein. 
Some old cells of T. pokitum were infested by mites, 
probably Pediculodes ventricosus Newport, but since 
there was slight mortality in this lot of material I pre- 
sumed that the mites had come after the emergence of 
the wasps to feed upon any old spiders which chanced 
to be there; several individuals of the Tachnid fly, Sar- 
comacronychia trypoxylonis, were reared from these 
mud cells by C. H. T. Townsend. Pseudagenia mellipes 
makes her own mud nest within the abandoned cells (as 
shown by arrow in fig. 63). I have also found their 
abandoned cells used by 7. clavatum; these did not re- 
move the heavy cocoon, but lined it smoothly with a thin 
layer of mud. Pseudagenia adjuncta also made small 
mud cells within the old cocoons remaining in the nests, 
and the bees, Osmia cordata, plastered and resealed the 
old cocoons in the nests with a waxy substance (see 
fig. 64). 
A study of a collection of nests of 7. politwm compris- 
ing 1282 cells gave some interesting evidence on the 
vigor of the species, and some indication of variation 
or defect in instinct. It was cheering to find that 972 
of these, or 76 per cent, gave forth good adults in the 
spring after wintering in the cells. In 126 cases (10 
per cent) the mothers had erred in failing to provision 
the cell or to oviposit, while an additional 27 cells had 
