128 
Psyche 
[September 
After the spider has been alerted two things may occur. If the 
prey is in a state of sustained vibration the spider almost always 
makes an immediate approach to it. If on the other hand, the prey 
is immobile or merely making spasmodic movements the spider usually 
plucks the web. If the prey has remained in the web until the spider 
plucks, this behavior is likely to be followed by an approach to the 
prey (during which the plucking movement may be repeated). 
When the prey escapes after the initial alerting impact, the spider 
usually returns to its pre-alerted state after plucking. 
As examples of the simplification involved in our model we can 
cite the following examples that occur in the fairly complex section 
that we have traced so far. Thus a further alternative behavior 
that can occur on the impact of prey is not shown. Instead of the 
spider being alerted it may show an immediate escape response. This 
usually takes the form of the spider running upwards from the hub, 
out of the web and onto the support lines (or even onto nearby 
vegetation). Similarly, if it did not result in an illegibly complex 
diagram, we could show at least three distinct approach-to-prey 
behaviors. There is a rapid, unhestitant, approach that is made to 
rapidly vibrating insects and a hesitant, much interrupted by pluck- 
ing, approach to non-vibrating insects. In addition very large or 
very heavy insects are approached in a slow ‘deliberate’ manner, in 
which legs I & II are flexed far back over the prosoma in a very 
characteristic ‘cautious’ gait. 
After arrival at the prey the spider may immediately attack with- 
out a perceptible pause, or may touch (with the tarsi) and palpate 
(with the pedipalps) the prey, before attacking. We have not shown 
these ‘investigative’ stages in our diagram. 
There are three basic attack behaviors, all of which involve the 
use of the chelicerae. In no case have we ever seen Nephila clavipes 
(or any other species of Nephila , for that matter) use the strategy 
of attack wrapping. This matter is extensively discussed by Robin- 
son, Mirick & Turner (1969). The three basic forms of biting 
attack are as follows: 
1. An attack similar to the seize and pull out behavior of Argiope 
argentata (see Robinson & Olazarri, 1971). This is given to very 
small or light prey. 
2. A long bite in which the bite is not immediately followed by 
pulling out movements but is sustained in situ. This long bite may 
be accompanied by a special posture in which legs I & II are raised 
off the web and the opisthosoma is raised at its apex so that the 
body presents a concave dorsal aspect. 
