1977] 
Robinson & Robinson — Flies and Spiders 
153 
dabbing at the liquid with their extended mouthparts. They quickly 
became swollen with food and their abdomens in particular were 
distended and almost spherical. The intersegmental membranes 
became very clearly visible and extended. After feeding the flies 
returned to the spider’s cephalothorax. This timing of movement 
onto the prey item to coincide with its liquifaction seems to be fairly 
precise. It occurred in five out of five instances in which we pro- 
vided the spider with prey and watched the whole process from its 
inception. The spider on which we made these observations dis- 
appeared after four days and we replaced it (on the still-intact web) 
with an adult female Argiope argentata. Two flies settled on this 
spider and fed once on her prey before disappearing. (It is note- 
worthy that the Argiope was able to locate and successfully attack 
prey on the structurally very different Nephila web. This has pro- 
vided us with a useful tool for further studies of araneid predatory 
behavior.) 
We saw very few cases where the spider reacted to the presence 
of the flies. Araneids seem to make very few responses to the ac- 
tivities of their larger kleptoparasitic associates, the theridiids of 
the genus Argyroides (see Robinson & Olazarri, 1971:34-5; Robin- 
son & Robinson, 1973:32). 
Argiope savignyi and unidentified flies 
While carrying out observations on Argiope savignyi in an in- 
sectary at Curundu, Canal Zone, Panama, the prey of two separate 
adult female spiders was visited by flies that did not alight on the 
spider at any stage. The flies “appeared from nowhere” and fed 
on liquifying prey items from which the spider was simultaneously 
feeding. On one occasion the spider’s prey was a pentatomid and 
the entire insectary in which we were working was flooded with the 
penetrating odor of the hemipteran’s defensive secretion. In the 
second case (Figure 2), the prey was a moth. In both instances the 
flies alighted on the spider’s prey and never moved onto the spider 
at any stage. After feeding they simply flew off. We were unable 
to catch the three flies involved. 
Argiope argentata and Conioscinella sp. 
While censusing Argiope argentata along the Old Gamboa Road, 
Summit, Canal Zone, we found an adult female of this species con- 
suming a half-digested acridiid. On this prey were two small flies 
