Empty Gonometa postica cocoons function as nest sites and shelters for arboreal ants

Abstract

Arboreal ants use a variety of plant structures as nesting sites, but may also nest in structures created by arboreal ecosystem engineers. We observed, for the first time, ants using empty cocoons of the economically important silk moth species, Gonometa postica, as shelter and nesting sites. Individual trees and individual cocoons were occupied predominantly by one dominant ant species, although in some cases by co-occurring ant species. Ant abundance and occurrence were positively related to cocoon size and the presence of scale insects on branches of the trees, and negatively influenced by cocoon occupancy by other invertebrates. Ants also preferred cocoons containing only small parasite holes as opposed to cocoons containing large moth emergence holes, suggesting that ants select cocoons based on cocoon characteristics. Further, these results reveal that other arboreal invertebrates appear to benefit from cocoon production. Empty cocoons could be functioning as nest sites and shelters for arboreal invertebrates, and they could create favourable habitats for other invertebrates on Vachellia erioloba. Therefore, G. postica acts as an autogenic ecosystem engineer and current silk harvesting practices, which partly rely on harvesting empty G. postica cocoons, may have potential local and large-scale implications for inter-specific interactions in these arboreal systems.