1978] 
Jackson & Smith — M alios and Dictyna 
79 
Acknowledgements 
For comments on the manuscript, we thank P. N. Witt, and M. C. 
Vick. Special thanks go to W. J. Gertsch for his assistance in the 
identification of spiders. C. E. Griswold, P. S. Jackson, and V. D. 
Roth are gratefully acknowledged for assistance in the field. The 
assistance of the Southwestern Research Station of the American 
Museum of Natural History is gratefully acknowledged. This work 
was supported in part by the North Carolina Division of Mental 
Health Services, Research Section and by N.S.F. grant number 
BMS 75-09915 to P. N. Witt. 
Summary 
Three types of social organization and three corresponding types 
of webs occur in the Dictynidae: solitary (individual webs); com- 
munal, territorial (web complexes); communal, non-territorial 
(communal webs). Solitary (M. niveus ) and communal, territorial 
(M. trivattatus, D. calcarata, and D. albopilosa) species were 
censused in nature; for M. gregalis (communal, non-territorial), 
free-living populations in communal webs in the laboratory were 
censused. Web surface area per spider decreases as one goes from 
solitary (ca. 35 cm 2 ) to communal, territorial (ca. 10 cm 2 ) to 
communal, non-territorial (ca. 2 cm 2 ) species. Very large popula- 
tions may occur on single web structures of communal species 
(estimates of maxima: M. trivittatus, 10,000 spiders; M. gregalis, 
20,000). There is a tendency for adult females to occupy nests and 
the interior of webs, with males and immatures occupying the 
exterior and the interstitial areas. Sex ratios (male:female) are 
skewed in favor of females (M. gregalis 1:7; communal, territorial 
species, 1:3; males of solitary species are infrequently found). 
References 
Burgess, J. W. 
1976. Social spiders. Sci. Amer. 234: 100-106. 
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Buskirk, R. E. 
1975. Coloniality, activity patterns and feeding in a tropical orb-weaving 
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