1968] 
Matthews — Microstigmus 
29 
glandular apparatus is very prominent in tergites treated with 10% 
KOH and viewed under high magnification. While the function of 
the gland is not yet known, it may prove to be the source of secreted 
material applied by the setal brush. 
Within the nest are the pocket-like cells, situated in the lower 
half of the sac 8 to n mm below the entrance. Initially they are 
arranged about the periphery of the nest, with the central area 
gradually filled as the number of cells increases. Each cell, approxi- 
mately cylindrical in shape, is about 4 mm long and 1. 8-2.1 mm 
wide at the mouth. Diagrams representing cell distribution and con- 
tents of a large and small nest are given in Figs. 8 and 9. 
A total of 139 cells (mean, 3.6 cells per nest) were found in 39 
dissected nests; the largest number of cells in a single nest was 18. 
All but 7 nests contained 4 or fewer cells; six nests contained no 
cells, but four of these also lacked adults, indicating that they may 
have been abandoned. Ten nests contained but one cell. 
The cell contents from night-collected nests are summarized in 
Table. 1. Typically a four-celled nest would contain one pupa, one 
mature larva, one fully provisioned cell with egg or newly hatched 
larva, and one partially provisioned cell. Indeed, no two cells of 
the same nest were ever found to be in the same state of develop- 
ment, a fact also noted for M. theridii (Myers, 1934), suggesting 
that only one cell is constructed and provisioned at a time. Even in 
a 13-celled nest that contained 10 adult females, only 2 cells had 
eggs (each at a distinctly different stage of development) and a third 
cell was partially provisioned. 
Cells of M. comes nests were mass provisioned with Collembola 
of the families Entomobryidae and Sminthuridae (Table 2). Use of 
Collembola as prey is, so far as known, unique to Microstigmus with- 
in the Sphecidae; however, they are an abundant and probably little 
exploited food source in the tropical rain forest.* The Collembola, 
averaging about 1 mm in length, were virtually all sub-adult; in 
completed cells with eggs, the number of Collembola per cell aver- 
aged 46 (range 31-58; N = 22). The prey are packed together 
into a compact, more or less spherical mass, but can be easily sep- 
arated in alcohol. Myers (1934) recorded predominantly Entomo- 
bryidae as prey of M. theridii on Trinidad, one cell containing about 
*Since this paper was written, I have received an unusual nest and adult 
of an undescribed species of Microstigmus from the same locality, in which 
the prey is thrips. The single provisioned cell contained 70 thrips, mostly 
immature instars. 
