340 
Psyche 
[June 
Table 1. Nest structure of Rubrica surinamensis 
Locality 
No. 
nests 
% multi- 
cellular 
Burrow 
length (cm) * 
Cell 
depth (cm)* 
Cali, Colombia 
22 
64 
11.8 (9-16) 
7.3 (5-9) 
Cafayate, Argentina 
12 
17 
16.8 (15-18) 
9.5 (8-11) 
Santa Maria. Argentina 
3 
0 
16.0 (15-18) 
9.2 (8.5-10) 
Las Termas, Argentina 
6 
0 
16.3 (14-22) 
10.5 (8-13) 
* Mean and range of variation. 
separated by only 1-4 cm of soil. It is, of course, possible that the 
unicellular nests we dug out might have had more cells added (ex- 
cept for one that had received the final closure) . Four of the 2- 
celled nests and two 3-celled nests had received the final closure 
when excavated. In multicellular nests, the earlier cells invariably 
contained cocoons, but it was usually possible to trace the filled bur- 
rows to these cells because the fill was not as compact as the sur- 
rounding soil. 
However, only 2 of 21 nests in Argentina were bicellular and none 
had more than two cells ; one of the 2 bicellular nests was in the hard 
soil of the schoolyard at Yacochuya. There is a general tendency for 
wasps nesting in firm soil to make shallower nests and to prepare 
more than one cell per nest. Thus it would be rash to assume that 
these differences between the Colombian and Argentinian populations 
had a genetic basis. 
There is no evidence that an inner closure, separating cell from 
burrow, is maintained at any time. However, an outer closure is 
normally made whenever the female leaves the nest. We noted no 
exceptions to this in Colombia or Argentina, but occasional individu- 
als in Trinidad did omit the outer closure. This was also noted in 
Trinidad by Vesey-Fitzgerald (1940), who believed that closure was 
usually omitted when the larva was large. 
Provisioning the Nest 
There are many published records of Rubrica surinamensis preying 
upon flies, and our own records confirm the fact many kinds of flies 
of small to moderate size are accepted (Table 2). The flies are 
evidently killed by the sting. The egg is laid erect on the side of 
the first fly placed in the cell, and provisioning is progressive. 
The flies taken are apparently those readily available near the 
nesting site. Belt (1874) observed females pursuing horseflies around 
