1974 ] Evans, Matthews J & Callan — Rubrica surinamensis 341 
livestock and humans, and Callan (1945) reported the capture of 
engorged stable-flies, one nest having been provisioned entirely with 
stable-flies. The frequent use of stable-flies and Tabanidae in Trini- 
dad probably reflects the fact that the cattle pens of the Imperial 
College of Tropical Agriculture were not far away. All specimens 
of Tabanidae and Muscidae from this site were females. On the 
other hand, the records of Syrphidae included males as well as fe- 
males, suggesting that they were taken on flowers. There were many 
cattle near the nesting site at Cali, again possibly serving as a source 
of Muscidae, although no tabanids were found to be used as prey at 
this site or at any of the localities in Argentina. 
We observed several females hunting beeflies at Santa Maria, 
Catamarca, Argentina (RWM, note no. C38). These wasps flew 
about flowers growing in the sand, apparently hunting flies visually. 
Having located a beefly, the wasp would hover some 30-40 cm be- 
hind it, about 15 cm above the sand, and follow the fly until it 
landed on a flower. Then it would dash suddenly at the fly, some- 
times producing an audible clash. However, although more than 20 
attempts to take beeflies were observed, in every case the fly darted 
almost straight up at the last moment and escaped from the wasp. 
The infrequent use of beeflies as prey (Table 2) may reflect their 
lack of success with flies of this group. At Santa Maria, Rubrica 
females were also seen to dash after Microbembex wasps visiting the 
flowers, again unsuccessfully. 
The way in which the prey is carried to the nest is similar to that 
of other bembicine wasps. It is held firmly by the middle legs, 
ventral side up and with the head forward. Since the wasp must dig 
through the small pile of soil over the entrance, as much as 20-60 
seconds may be required to gain entry (Fig. 2). As the wasp enters, 
the prey slides backward and the grasp is shifted to the hind legs, 
whereupon wasp and prey disappear down the burrow. However, 
flies are occasionally dropped or become stuck in the entrance. In 
such cases the wasp enters the nest, turns around inside, and comes 
out and drags the prey in with her mandibles. On leaving, the wasp 
makes a quick closure, then flies about briefly and returns one or more 
times to scrape soil over the entrance. 
Both at St. Augustine, Trinidad, and Cali, Colombia, we noted 
instances in which females carrying prey were pounced upon by 
other females. This usually resulted in the females struggling on 
the ground and ended by one escaping and diving precipitously into 
her nest with the prey. 
