Why do male tree weta aggressively evict females from galleries after mating?

The sexually dimorphic Wellington tree weta (Hemideina crassidens Blanchard) (Orthoptera: Anostostomatidae) is a harem-defending polygynous insect in which males use their enormous mandibles to fight conspecifics for access to harems residing in tree cavities (gallery). Tree weta ejaculates (spermatophores) do not include a nuptial meal (spermatophylax) to delay removal by females as in some ensiferan Orthoptera. Consequently, male tree weta are predicted to remain with their mates post-copula to ensure complete sperm transfer. Contrary to prediction, however, males forcibly eject females from the mating site (gallery) soon after copulation. Results suggest that forcible ejection occurs apparently because females consume the previous spermatophore if either the resident male or a rival initiates a subsequent copulation attempt. Thus, ejection appears to reduce the resident male's risk that his ejaculate will be eaten and his mate will copulate with another male.