130 
Psyche 
[Vol. 90 
Table 2. Spider selectivity (E^) values for prey types collected from webs of A. 
tuonaho. 
Prey type 
Collected from webs 
(eaten only) 
no. rj 
Collected from webs 
(eaten and uneaten) 
no. Pi 
Es 
Beetles 
52 
18.8 
56 
12.5 
+0.20 
Nematocerous Diptera 
32 
1 1.6 
164 
36.8 
-0.52 
Non-nematocerous Diptera 
28 
10.1 
34 
7.6 
+0.14 
Ants 
116 
42.0 
128 
28.7 
+0.19 
Parasitoid Hymenoptera 
32 
11.6 
42 
9.4 
+0.10 
Others 
16^ 
5.8 
22** 
4.8 
♦Others include: butterflies (6), bees and wasps (10) 
♦♦Others include: butterflies (6), bees and wasps (10, leafhoppers (4), thrips (2) 
numbers of eaten (32) and uneaten (132) individuals to permit com- 
parison. Mean body lengths for eaten (x = 1.6 mm; SD = 1.8) and 
uneaten (x = 0.8 mm; SD = 0.29) nematocerans were significantly 
different (t = 4.86; p <.00 1). 
Discussion 
The present findings highlight 2 features of the predatory behav- 
ior of A. tuonabo. First, the webs captured and the spiders con- 
sumed nonrandom samples of the available prey. Nonrandom web 
captures have been recorded for other spiders (e.g. Uetz and Biere 
1980; Brown 1981; Turnbull 1960) and most likely reflect differing 
abilities for web avoidance or escape among different prey. While 
no avoidance was observed, 1 did see several large flies (Asilidae and 
Tabanidae) strike webs but then successfully escape. Among insects 
successfully restrained by the web, the spider may attack, ignore, or 
reject different types and/or sizes of prey. Numerous studies (e.g. 
Robinson and Robinson 1970, 1973; Riechert and Tracy 1975; 
Turnbull 1960) note rejected prey, but few studies (Uetz and Biere 
1980) quantify attack vs. ignore probabilities for different prey. 
Here, the tendency of A. tuonabo to ignore nematocerans probably 
does not reflect avoidance but rather the inability of these small, 
weak-flying insects to escape or damage the web. Thus, A. tuonabo 
may have ignored these weak prey only to consume them with their 
web in the evening. Interestingly, the mean body length of nema- 
tocerans being consumed was nearly twice that of nematocerans 
