1975] 
Tolbert — Avoidance Behavior in Orb Weavers 
31 
(<5%) the abdomen was touched. I positioned myself approxi- 
mately 0.5- 1. 0 m either directly behind or directly in front of the web 
depending on the direction of model presentation to be used. In 
employing this model the assumption was made that all spiders tested, 
regardless of instar and species, recognized the model as a predator. 
Data on construction of barrier webs or “tangles” and the nature of 
stabilimenta were gathered throughout the summer in an attempt to 
assess possible anti-predator functions. The chi-square test and Cox 
and Stuart test for trend were used in the statistical analyses. The 
taxonomy of Argiope follows Levi (1968). 
The Web 
The orbs of A. aurantia and A. trifasciata are “typical” araneid 
webs, consisting of foundation lines, radii, spirals, a free zone and a 
hub. Neither species constructs a retreat. The spider is normally 
located at the hub in a head-down position. The web is inclined 
slightly from the vertical and there may be several stabilimenta bands 
in or near the hub (fig. 1). Up to two barrier webs (fig. 2) may 
be associated with each orb web. 
Barrier Webs 
Barrier webs or “tangles” were frequently constructed by A. tri- 
fasciata and to a lesser extent by A. aurantia. Essentially a barrier 
web is an irregular non-viscid silk mesh connected to the orb web 
and nearby vegetation or other supports. There can be up to two 
such tangles, with the primary barrier web positioned behind the 
dorsum of the spider. The secondary barrier, which is nearly always 
smaller, is located on the other side of the orb (fig. 2). In early 
instar A. trifasciata the primary barrier web is quite cone-like with 
the orb forming the base of the “cone”. A small gap is left at the 
bottom of the orb and the cone through which the spider may drop 
if disturbed. Since these barriers are connected to the outer edge of 
the orb, disturbances (vibrations) are transmitted to the spider. It 
is generally thought (Comstock, 1948; Gertsch, 1949 and Marples, 
1969) that they serve some defensive function. My experience with 
these two species confirms this observation. In paint marking spiders 
on the dorsum I have often accidentally touched the barrier web, 
alerting the spider and making it more difficult to mark. In addition 
to an early warning function, the barrier webs, particularly the pri- 
mary barrier, constitute a physical obstacle to invertebrate predators. 
Such barriers reduce the direct points of entry that predators might 
