1971] 
Robinson Cff Alirick - — Nephila clavipes 
125 
they were killed by freezing to avoid contamination by chemical 
killing agents. Behavioral observations were supplemented by cine- 
photography and the duration of behavior units was recorded on a 
Rustrak multi-channel chart recorder. 
Natural History 
In Panama, and wherever we have encountered Nephila clavipes 
in South America (Colombia & Venezuela), the spider is most fre- 
quently found at the edges of forest clearings, alongside forest trails 
and across forest streams and watercourses. It thus apparently ex- 
ploits areas within the forest that are in all probability flightpaths 
of insects. The structure, size, and siting of N, clavipes webs is 
consistent with the view that the spider specialises on prey that are 
in flight above the herb layer rather than moving about in it. Al- 
though the web may be sited with part of the prey capture area 
within the herb layer it is most frequently above this or stretched 
across gaps in the vegetation. The structure of the web has been 
described by Gertsch (1948) and Peters (1954, 1955). For its 
area, which is large, the web has a very fine mesh which is far less 
penetrable by small insects than the much smaller but coarse-meshed 
web of Argiope argentata (Fabricius), as was shown by Robinson, 
Mirick Sc Turner (1969). The web of the adult spider is not a 
complete orb but is U-shaped with the hub very close to the upper 
bridge thread. Kaston Sc Kaston (1953, p. 176) give an excellent 
figure of the N. clavipes web. Webs of several adult spiders are 
often built in close proximity and fairly large aggregations of the 
spider may occur in apparently favourable areas (Shear 1970, has 
commented briefly on this phenomenon). 
The adult web is frequently equipped with a barrier web con- 
sisting of a complex of strong lines arranged in a non-symmetrical 
manner above and/or below the main plane of the orb. There is 
considerable variation in the structure of barrier webs. Robinson 
Sc Robinson (1970) have suggested that they may function as early 
warning devices enabling the spider to detect the approach of pos- 
sible predators. Certainly the spider often responds to manipulation 
of the barrier web by escape or other forms of defensive behavior. 
Web renewal is not a daily occurrence, and in captivity the spider 
may only renew part of the web at a time. (This is also certainly 
the case with free-living N. maculata but we have not made exten- 
sive observations on web renewal by free-living N. clavipes ). 
Our observations on the natural prey of N. clavipes , although 
limited in scope, confirm the deductions based on web structure and 
siting i.e. that flying prey of small to medium size may be the 
