66 
Psyche 
[March 
species (M. trivittatus Banks, Dictyna calcarata Banks, D. albopilosa 
Franganillo) live in web complexes. Web complexes consist of 
variable numbers of web units, each consisting of a nest and a mesh; 
and web units are connected to each other by strands of silk in the 
interstitial web. Evidently, web units are treated by the occupants as 
defended territories (Jackson, 1978a). In the communal, non- 
territorial species ( M . gregalis Simon), groups of spiders live in 
communal webs which consist of surface sheets with holes leading 
into the interior. The interior contains nests, tunnels and supporting 
lines connecting the sheet with the substrate beneath (see Burgess, 
1976; Diguet, 1909a, 1915). Communal webs are not divided into 
defended units as in web complexes. More detailed information 
concerning social organization, web characteristics, and habitats is 
provided elsewhere (Jackson, 1978a). 
Methods 
DATA FROM NATURAL POPULATIONS 
For census areas, locations were chosen which seemed to have 
particularly high densities of spiders. The census areas for Mallos 
niveus O. P. Cambridge were one-dimensional (horizontal lines). 
All other census areas were rectangular. For D. calcarata and 
Censuses 3-6 for M. trivittatus, complete web complexes of relatively 
small size were used; and the boundaries of the census areas were 
chosen to closely correspond to the edges of the web complexes. The 
distance from each spider in the complex to the nearest conspecific 
in the vicinity but not in the complex was greater than twice the 
diameter of the complex in each of these census areas. For Census 
No. 1 and 2 for M. trivittatus, each area censused was part of a large 
web complex. 
The corners of each census area were marked with pieces of tape. 
Each web or web unit was completely searched, a process that 
destroyed the web unit. The occupants of the units were recorded; 
and a piece of tape, with a code number, was placed at the location 
of each occupied nest before it was destroyed. The distance of each 
of these nests to its nearest neighboring nest was measured. 
The exact locations of spiders on the sheet and interstitial webs 
proved excessively difficult to measure accurately. This was because 
they were frequently obscured from view by silk and debris; and the 
process of locating spiders inevitably disturbed them, leading to 
