1969] 
Robinson — Predatory Behavior 
497 
capture efficiency of the two webs for small insects. Thus (basal 
columns, Figure i), 15.5% of the Trigona flew straight through the 
Argiope webs, missing the viscid spiral, or touching the web mo- 
mentarily. Only 2% of the Trigona passed through the Nephila 
webs. Since we started, in all cases, with fresh webs, this result 
is not likely to be biased by the effects of the prey arriving early in 
the sequence on the state of the web for later arrivals. In fact, in 
the Argiope results, escapes through the webs in the first five of the 
sequence were in the relationship 17:14 compared with escapes in 
the second five of the sequence. 
The second columns in each graph show the number of escapes 
occurring after the prey were in the web and an analysis of the 
behavior of the spider at the time the prey escaped. Argiope missed 
only 24.5% of the prey striking the web whereas Nephila missed 
40.5%. If we add losses through the web to these figures we find 
that Argiope lost 40%, and Nephila 42.5% of potential prey flying 
at the web. In addition, as mentioned earlier, Nephila incurred 
further losses of captured prey when it rushed into attack carrying 
these prey in its jaws (having omitted post immobilization wrap- 
ping at the feeding site). An additional 3.5% of prey were lost in 
this way. The total absolute losses for Nephila were thus 46%. 
The fact that 15.5% of the bees passed through the Argiope web 
meant that this spider was under reduced pressure during the five 
minute experimental period compared with Nephila. However, analy- 
sis of the data shows that Argiope achieved a very considerable 
acceleration of predatory behavior under the conditions of the experi- 
ment, and became significantly faster than Nephila (see Table 1). 
A substantial part of this reduction was achieved by the omission of 
the cut out, carry, and wrap at hub stages and is therefore a striking 
illustration of the advantage of being able to leave immobilized prey 
in situ. Prey losses by Nephila occurred principally when it was 
performing activities at the hub (post immobilization wrapping and 
turning to resume its normal head down position). The attack 
phase (biting) was usually completed by the time the next prey ar- 
rived. A surprising number of escapes occurred while Nephila was 
locating the prey (i.e., at the pluck stage). These losses may be 
attributable to the fact that prey location did not occur at the 
moment of impact but was delayed by preceding activities until the 
prey had almost freed itself. Argiope was back at the hub, unen- 
cumbered by prey, when nearly half of the losses occurred. It seems 
quite possible that, in this case, the presence of numbers of wrapped 
prey in the web may complicate further prey location. We also got 
