1980] 
Trail — Predation by Argyrodes 
351 
were occupied by communal P. oweni, 50% (10 of 20) of the 
Argyrodes observed were found in communal groups. The dif¬ 
ference between the distribution of Argyrodes expected, given the 
proportion of solitary and communal web sites, and that actually 
observed is significant at p < 0.05. (Expected number of Argyrodes 
in communal groups is 0.28 X 20 = 5.6; expected number in solitary 
webs is 14.4; observed values are 10 and 10; chi-square = 4.80, 1 d.f.) 
Although 1 observed too few cases of actual predation to perform 
statistical analysis, the same trend is seen. A disproportionate 
number (4 out of 8 or 50%) of the observed predatory events 
occurred in communal groups. 
Discussion 
Spider Predation By Argyrodes 
Other spiders are a significant element in the diets of Argyrodes 
fictilium and A. baboquivari. In particular, A. baboquivari is one of 
the most conspicuous predators on P. oweni in the Chiricahuas. 
The methods used by the more strictly kelptoparasitic Argyrodes 
may preadapt them for predation on the host itself. Legendre (1960) 
believed that Argyrodes kleptoparasites avoid attack from their 
hosts by recognizing their approach and quickly moving away. 
Vollrath (1976, 1978, 1979) showed that the host’s prey wrapping 
motions produce distinctive vibrations in the web, which Argyrodes 
elevatus Taczanowski uses to locate the captured prey items. The 
use of these host-generated signals both to determine the location of 
the host in the web and to avoid attack could preadapt the 
Argyrodes for safely stalking and capturing the host herself. 
Large body size, relative to that of the hosts, could also act to 
make predation on hosts more feasible. Kleptoparasitic Argyrodes 
tend to be smaller than their hosts. For example, females of A. 
elevatus and A. caudatus (Taczanowski) are about 3.4 mm and 3.5 
mm long, respectively (Exline and Levi 1962) while their araneid 
hosts, Nephila clavipes (Linnaeus) and Argiope argentata (Forskal), 
are 12-16 mm and 22 mm long (Kaston 1978). On the other hand, 
those Argyrodes that are known to prey on other spiders are the 
same size or larger than their hosts. For example, females of A. 
baboquivari are about 3.7 mm long and females of A. fictilium are 
5.5-12.00 mm long. Prey species such as Philoponella oweni are 
4.7-7.1 mm long (Opell 1979) and females of Frontinella communis 
