78 
Psyche 
[March 
majority of observed instances of pluck-walking involved males on 
the surfaces of webs. 
We have no information at this time concerning how new 
communal webs are formed by M. gregalis. One possibility is that 
new webs are founded by single adult females or by groups of 
several adult females. In the laboratory web censuses (method 1), 
the webs with fewer spiders (predominantly adult females) may 
have been ones that were newly founded. Those with more spiders 
and a greater proportion of smaller immatures may have been older 
webs in a period of rapid growth. Further study, especially in the 
natural habitats of these spiders, is necessary. Information is also 
lacking on the formation of web complexes by M.trivittatus and D. 
calcarata. 
CAUSES OF SKEWED SEX RATIOS 
The causes of the relative rarity of males in all species investigated 
are unknown. We do not know the sex ratios at hatching. If maternal 
investment in progeny of the two sexes is equal, we would expect a 
1:1 ratio (Fisher, 1930; but see Hamilton, 1967; Trivers and Willard, 
1973). There are a number of factors that might skew the adult ratio 
in favor of females even if the ratio at hatching is 1:1. Earlier studies 
(Jackson, 1978b) suggested that adult males of solitary and com- 
munal, territorial species are relatively nomadic, expending con- 
siderable time and energy wandering about searching for females. 
As a result, a sizeable proportion of the males in populations of 
these species might not be found in censuses of webs. Also, the 
nomadic character of males might subject them to earlier mortality 
from predation, starvation, and other factors. Shorter male longev- 
ity would skew the adult sex ratio in favor of females. However, 
mortality factors such as predation would seem less important for 
M. gregalis populations in the laboratory; yet the sex ratio was 
skewed in favor of females here also, suggesting that mortality 
factors of a more intrinsic nature might be involved. Females of each 
investigated species oviposited several batches of eggs over a period 
of time. In contrast to females, males may be adapted to a lifestyle 
that emphasizes courtship, mating, and searching for females, in 
conjunction with greater vagility and smaller size, at the expense of 
maintenance functions that would serve to prolong survival. 
