1987] 
Uetz & Hart sock — Micrathena gracilis 
109 
present in window-pane traps, which probably affects the accuracy 
of the latter (Robinson and Robinson 1970). 
The design of our ASW’s differs from that of previous studies in 
construction, area, mesh structure, and thread thickness. In compari- 
son to Chacon and Eberhard (1980), ours more closely resembled the 
structure of actual spider webs, due to the presence of “radii”, and 
thread thickness of 0.22 mm, (theirs was nearly 1.0 mm thick). This 
reduced the visibility of traps, an especially important consideration 
when studying diurnal orbweavers. Even though the “radii” of our 
traps were sticky, we believe that their presence is important since 
insects are often only capable of detecting and avoiding webs, after it 
appears that they are going to strike it (Turnbull 1960; Buskirk 1975; 
pers. obs.). If an insect is able to detect individual threads and alter its 
course to avoid a collision (or fly mistakenly into another sticky 
thread), it will probably do so because the thread is there and not 
because it may or may not be sticky. The elimination of “radii” from 
ASW traps could alter the flight behavior of small insects that are 
capable of flying through wider meshes in a way that is different than 
if they were present. Because the function of these devices is to 
intercept flying insects in nearly the same manner as spider webs, 
Chacon and Eberhard (1980) may be too harsh in their criticism of 
ASW’s as mimics of spider webs. Even in illuminated areas, insects 
were only occasionally seen to avoid both spider webs and ASW’s, 
and the capture rate for ASW traps was as high as or higher than that 
of the webs under observation. We would expect capture rates of 
ASW’s to be lower than those of spider webs if the visibility of the 
traps affected their intended function. Consequently, while not being 
exact mimics of spider webs, ASW traps are reasonably effective 
sampling devices for flying insects in a forest understory. While some 
authors have discouraged their use (see Chacon and Eberhard 1980) 
and ASW’s may not be suited for use in all environments, we feel that 
they can effectively sample the potential prey of many orb-weaving 
spiders better than conventional sampling methods (see Uetz and 
Biere 1981 for field comparisons). 
A comparison of web catches with ASW’s will reveal if the web of 
the spider contributes to dietary selectivity. Data from observations, 
and from web traps placed nearby while observations were being 
made, were analyzed using an index of dietary specialization — the 
