1971] 
Robinson C 5 f Mirick — Nephila clavipes 
127 
Predatory Behavior 
1. The basic pattern 
Figure 1 is a summary diagram of the complex of possible se- 
quences of predatory behavior that we have observed to be given by 
adult female N. clavipes to a variety of prey presented in several 
ways. It has the same summary function that Figure 2 of Robinson 
(1969) had in relation to the behavior of Argiope argent ata and 
is not meant to be a flow diagram or relate to any cybernetic con- 
ventions. It does, however, illustrate the temporal sequence and 
relationships between behavior units, their degree of association, and 
the effects of some stimuli on the course of the sequence. Like most 
models it is certainly much more simple than reality. 
In the predatory behavior of N. clavipes alternative behavior units 
are available at several functional stages and the ‘decision’ to employ 
one or other of these is shown, on the diagram, to be the result of 
a discrimination. We recognise that in some cases our assumption 
of the basis (or bases) for the discrimination may be an oversimpli- 
fication; this matter is discussed at the appropriate place in the text. 
The diagram employs simple conventions. The behavior units 
are shown as circles connected by lines. The arrows on the lines 
show the direction of change from one behavior unit to the next. In 
the upper half of the diagram two conventions are used to denote 
‘choice’ points. Some of the circles are divided into two halves by 
vertical lines so that two behaviors may follow the behavior shown 
by the circle. In addition, here and throughout the diagram, small 
square boxes on the lines connecting behavior circles represent places 
where behavior may be switched from one course to another. Dotted 
lines from oblong boxes suggest imputs to the system that are de- 
pendent on stimulus properties of the prey. 
Behavior occurring up to first contact with the prey is shown in 
a much simplified form. The activity spider on hub (which could 
be amplified as ‘spider at hub in predatory position waiting for prey’) 
is represented as an ongoing activity by a vertical line beneath the 
behavior circle. If a prey item, or in fact any item above a certain 
weight, strikes the web the spider is alerted (the square box has an 
imput from prey strikes web and an output to spider alert , this 
represents a diversion from the ongoing activity spider at hub). The 
overt behavioral change following impact may be a momentary in- 
crease in the flexion of the spider’s legs prior to an almost immediate 
movement towards the prey or a more sustained adoption of this 
alert position. 
