1978] 
Jackson & Smith — Mallos and Dictyna 
73 
SEX/AGE CLASS RATIOS 
Based on the spiders in the two censuses in the culvert at E. 
Turkey Creek, this large web complex was estimated to have had a 
population consisting of 27% adult females, 9% adult males, and 
64% immatures. The adult sex ratio (Male: Female) was approxi- 
mately 1:3. Based on the censuses at Chapala, populations of D. 
calcar ata in web complexes on buildings were composed of 14% 
adult females, 5% adult males, and 81% immatures; and the adult 
sex ratio was 1:3, as for M. trivittatus. No males were found in the 
censuses of M. niveus. Generally only small numbers of males of the 
solitary species were found, and these were predominantly ones in 
webs with females (Jackson, 1977b). 
Based on the 19 censuses of M. gregalis by Method No. 1 
(disassembly), population composition was 29.8 ± 25.49% adult 
females, 4.1 ± 5.97% adult males, 17.6 ± 12.17% large immatures, 
and 48.2 ± 27.41% small immatures. Immatures comprised a greater 
proportion of the spiders in webs with large population size (Table 
2). The average adult sex ratio was approximately 1:7. For the 33 
transect censuses (Method No. 2), population composition was 12.3 
± 7.44% adult females, 3.0 ± 3.85% adult males, 38.0 ± 12.96% large 
immatures, and 46.2 ± 13.11% small immatures (adult sex ratio, ca. 
1:4), with a total of 16.8 ± 2.34 spiders occurring in each census. The 
three sections of the web were comparable. 
Discussion 
AGGREGATION SIZE AND DENSITY — 
EVOLUTIONARY CONSIDERATIONS 
The occurrence in certain areas of very large populations of some 
species, especially M. gregalis and M. trivittatus, and the great 
densities of spiders within these populations contrast markedly with 
the majority of Dictyna and Mallos species. Most species are 
solitary, with individuals living in relatively widely spaced indi- 
vidual webs on stems and leaves of vegetation (Jackson, 1978a); and 
although density censuses were not carried out for these, our 
impression is that an area of 50 to 100 m 2 in a population of a 
solitary species would usually contain fewer than a dozen indi- 
viduals. In contrast, the largest web complex of M. trivittatus 
occupied approximately this much space and contained more than 
10,000 individuals. 
