Animals often face conflicting demands when making movement decisions. To examine the decision process of social animals, we evaluated nest site preferences of the social spider Stegodyphus dumicola. Colonies engage in collective web building, constructing three-dimensional nests and two-dimensional capture webs on trees and fences. We examined how individuals and groups decide where to construct a nest based on habitat structure and conspecific presence. Individuals had a strong preference for three dimensional-substrates and conspecific presence. Groups were then provided with conflicting options of three-dimensional substrates vs. two-dimensional substrates with a conspecific. Groups preferred the three-dimensional structures without pre-settled conspecifics over a two-dimensional substrate with conspecifics. When a group fragmented and individuals settled on both substrates, the minority group eventually joined the majority. Before rejoining, the collective prey capture behavior of divided groups improved with the size of the majority fragment. The costs of slow responses to prey for split groups and weak conspecific attraction may explain why dispersal is rare in these spiders.

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