1978] 
Jackson & Smith — Mallos and Dictyna 
69 
cave (ca. 1 m high and 1 m deep) made by an overhanging rock ledge 
in Big Thompson Canyon (Colorado, USA). 
Dictyna calcarata 
Census Area No. 1 (24 cm X 24 cm) and No. 2 (54 cm X 46 cm) 
were web complexes on the external walls of buildings in Chapala 
(Jalisco, Mexico). 
Results 
POPULATION SIZE AND DENSITY 
Densities for M. trivittatus and D. calcarata were relatively 
similar (Table 1). Since the M. niveus aggregations were linear (one- 
dimensional) it is problematic to compare densities in this species 
with the densities found in the other species. The webs of M. niveus 
in the census areas were oriented such that the shorter distance 
across each was vertical. The areas given in Table 1 were obtained 
by multiplying the length of the aggregations by 3 cm, the mean 
widths of M. niveus webs found on buildings (Jackson, 1978a). M. 
gregalis tends to live in higher densities. The webs censused by 
Method No. 1 (Table 2) had a mean density of 0.5 ± 0.66 spiders per 
cm 2 and 0.2 ± 0.14 per cm 3 . 
Based on many hours spent in the culvert at E. Turkey Creek, it 
seems that the densities obtained in Census Nos. 1 and 2 for M. 
trivittatus were representative of the large complex in the culvert. 
Using the mean of the two densities for spiders (14.23 per 1000 cm 2 ), 
webs (9.79 per 1000 cm 2 ), and occupied webs (8.79 per 1000 cm 2 ) as 
estimates for the densities for the complex as a whole, this web 
complex contained 10,200 spiders, 7,700 webs, and 6,500 occupied 
webs. This was by far the largest web complex of this or any other 
species in this study. 
Web units of M. trivittatus tend to be 5 cm X 4 cm; those of D. 
calcarata tend to be 3 cm X 2 cm; and webs of M. niveus on walls of 
buildings tend to be 4 cm X 3 cm (Jackson, 1978a). In the culvert on 
E. Turkey Creek, the interstitial area between web units tended to be 
quite small, since the mean for nearest neighbor distance was not 
much greater than the diameter of web units (Table 1). In all other 
censused web complexes, web units tended to be 2 to 4 web unit 
diameters apart; and aggregated M. niveus webs tended to be 2 to 4 
web diameters apart also. 
