Social organization of the colonial spider Leucauge sp. in the Neotropics: vertical stratification within colonies

A first step toward understanding why sociality has evolved in a particular taxonomic group is to establish comparison points by studying the organization of different social systems. We examined the social organization and spatial distribution of individuals in colonies of the undescribed colonial spider Leucauge sp. (Araneae: Tetragnathidae). The social organization of this species was typical of a colonial species, with spiders maintaining individual territories (orb webs) within a scaffolding of shared support lines maintained by the group. Furthermore, we observed a size-dependent vertical stratification of spiders within colonies, with large spiders occupying the highest positions, followed by medium, extra-small and small individuals, a spacing pattern that was consistent across colonies of all sizes. Spiders captured and consumed prey individually and displayed territorial behaviors involving web defense. This study provides a new example of a colonial spider species that shows a distinctive within-group spatial distribution. We discuss possible reasons underlying this species’ spatial arrangement in the context of social evolution.