1987] 
Tietjen, Ayyagari , & Uetz — Social spiders 
157 
Nest Material Fed-Upon Flies Non-Fed— Upon Flies Clean Silk 
(Silk with Flies) (Yeast Cultures) (Mixed Microflora) (Without Flies) 
Experimental Treatments 
Fig. 2. Mean visitation of grouped flies to paired experimental odors. For tests 
using Mallos gregalis silk (with and without flies), the silk provided the experimental 
odor while empty covered dishes were controls. Those tests using microorganisms as 
an odor source used sterile agar as the control. Asterisks indicate a significant differ- 
ence in visitation frequencies within a test (Chi Square and Wilcoxon Tests; p < .01). 
Those individuals with increased tolerance of neighbors would 
have a greater concentration of fly carcasses (and their associated 
yeasts) to attract prey. Further increases in interspider tolerance and 
eventual construction of a communal nest would provide additional 
concentration of prey attractants. The use of microbiota is not with- 
out disadvantages, however, since a large prey input may not be 
adequately fed upon by the spiders resulting in a shift to bacterial 
growth and an ammonia-based odor. Under such conditions the 
colony must abandon the nest and start construction anew. 
Acknowledgments 
This work was supported, in part, by a research grant from the 
National Science Foundation (BNS 79-10186 to W. J. T.). Speci- 
mens were collected during field expeditions funded by the National 
Geographic Society and the American Philosophical Society (grants 
to G. W. U.). We thank C. A. Meininger and M. J. Benton for 
assistance in the field, D. Fritz and M. Hodge for assistance in 
rearing spider colonies, M. Kaufman for SEM photography and 
preparation. 
