Silk threads function as an 'adhesive cleaner' for nest space in a social spider mite.

Individuals of the social spider mite Stigmaeopsis longus live communally in narrow, humid nests made from silk threads and display nest sanitation behaviour through the coordinated deposition of faeces. We used artificial dust to experimentally determine that females of this species use silk threads to perform regular cleaning of the nest space and eggs. We first learned that silk-weaving behaviour is not a by-product of nest building (nest reinforcement); rather, it is actively performed as a function of cleaning the living space and eggs. Furthermore, we determined the effectiveness of the attending females by artificially manipulating their natural habitat, which is clearly connected to the cleaning behaviour by parental females. As such, we have uncovered an extraordinary new role of silk threads as devices for cleaning the nest space and/or eggs. These results strongly indicate that special adaptations for maintaining clean habitats are essential for animals to evolve aggregative social lives.