1983] 
Shelly — Alpaicia tuonaho 
129 
Table I. Web selectivity (Ew) values for prey types collected from webs of A. 
tuonaho. 
Prey type 
Collected from webs 
(eaten and uneaten) 
no. rj 
Captured on traps 
no. Pi 
Ew 
Beetles 
56 
12.5 
320 
19.2 
-0.21 
Nematocerous Diptera 
164 
36.8 
337 
20.2 
+0.29 
Non-nematocerous Diptera 
34 
7.6 
453 
27.1 
-0.56 
Ants 
128 
28.7 
1 19 
7.1 
+0.60 
Parasitoid Hymenoptera 
42 
9.4 
264 
15.8 
-0.25 
Others 
22^ 
4.8 
175^^ 
10.4 
♦Others include: butterflies (6), bees and wasps (10), leafhoppers (4), thrips (2) 
♦♦Others include: butterflies (2), bees and wasps (2), leafhoppers (80), thrips (27), 
Hemiptera (8), Orthoptera (5), Collembola (3), Zoraptera (4), Plecoptera (3), 
Isoptera (21), Psocoptera (20) 
As the Es values imply, the majority (87%) of uneaten prey were 
nematocerous Diptera. Most of these, in turn, did not appear to 
have been wrapped. Many, in fact, were observed struggling in web 
while stuck by a single wing. Similarly, most uneaten non- 
nematocerous Diptera and parasitoid Hymenoptera were appar- 
ently unwrapped. In contrast, 9 of the 12 uneaten ants had clearly 
been attacked and wrapped. 
Only 2 groups, nematocerous Diptera and ants, were found in 
webs in sufficient numbers to allow meaningful calculation of web 
selectivity values for different size classes. Nematocerans less than 1 
mm were relatively more abundant in webs than on the traps, while 
the opposite was true for those between 1 mm-2 mm (Table 3a). 
Web selectivity values, however, did not differ greatly from zero for 
either size class. Ants in webs were rather uniformly distributed 
among 8 size classes (Table 3b). The majority (76.0%) of ants on the 
sticky traps, however, were less than 3 mm long. Consequently, web 
selectivity values for the 1 mm-2 mm and 2 mm-3 mm size classes 
were large and negative, while those for larger classes were all large 
and positive. 
Only ants were eaten in sufficient numbers to allow meaningful 
calculation of spider selectivity values for different size classes. Yet, 
since nearly all (90.6%) of the ants taken from webs were being 
eaten, these selectivity values provide little new information. Among 
the remaining groups, only nematocerous Diptera had large enough 
