1979] Uetz <& Burgess — Behavior in M. spinipes 85 
spiders were aggregated in any way in the willow shrub area, thus a 
social aggregation hypothesis is supported. 
The colonial web of Metepeira spinipes is a permanent aggrega¬ 
tion of individual prey catching orb webs in a matrix of communal 
space web. Burgess (1978) has suggested that cooperative behavior 
of “Social” spiders consists of simultaneous coordination of individ¬ 
ual effort on a task, like web-building. In M. spinipes the colonial 
web would appear to arise as the result of simultaneous or sequen¬ 
tial (but not coordinated) individual efforts at web building, rather 
than cooperative behavior. Prey catching orbs are spaced apart and 
each spider inhabits its own retreat. Although individuals may coex¬ 
ist at short distances, intruders on the spiral are met with agonistic 
behavior (Web shaking, chasing, etc.). In many solitary and aggre¬ 
gated spider species, maintenance of a personal space or territory by 
aggressive behavior has been shown (Buskirk 1975 and in press, 
Riechert 1978, Burgess 1978). The combination of solitary and 
colonial behaviors exhibited by this species suggests that it repre¬ 
sents an intermediate stage in the evolution of social behavior in 
spiders. 
In a colonial web like that of M. spinipes, where space webs are 
three-dimensional and highly interconnected, it is not possible to 
discern clearly the space web made by one individual vs. another. 
We measured the dimensions of polygonal colonial webs and 
counted individuals and orbs in the field, and from these we have 
estimated how the volume of the colonial web is subdivided by 
individuals (Fig. 2). The amount of space per individual in a colon¬ 
ial web decreases dramatically as colony size increases from 2-10 
individuals. However, in larger colonies, there appears to be a lower 
limit on the amount of space per individual. The asymptote in figure 
2 possibly reflects the minimal individual space requirements of M. 
spinipes. These values are probably underestimates of the actual 
amount of individual space, since there are often more individuals in 
a colony than there are orbs. The compressibility of individual space 
in aggregations of varying size shown by this species indicates a 
degree of tolerance of conspecifics beyond that expected if individu¬ 
als’ webs were merely attached to one another. 
Riechert (1978 and personal communication) has found that terri¬ 
tory size in a desert sheet web spider ( Agelenopsis aperta (Gertsch)) 
decreases with increased habitat quality over a wide range of areas. 
The size of the area occupied by an individual Agelenopsis spider is 
