Ant queens cannibalise infected brood to contain disease spread and recycle nutrients

Filial cannibalism, where parents eat their own offspring, is a taxonomically widespread behaviour with a multitude of potential adaptive explanations. Of these, the impact of parasites on the expression of filial cannibalism is particularly poorly understood. On one hand, cannibalising young with low survival probability may enable parents to reinvest valuable resources into future reproduction; on the other, cannibalising offspring harbouring parasites that can potentially also infect the parents may select against this behaviour. Although disease-induced cannibalism of eggs has been reported in fish, the benefits of consuming infected brood to contain infections - as an explanation for the evolution of filial cannibalism - remains largely unexplored. Here, we demonstrate that solitarily founding ant queens cannibalise all sick larvae in their nests before they become contagious, showing clearly that filial cannibalism both (i) contains an otherwise lethal infection without any long-term consequences on queen survival and (ii) enables the reinvestment of recouped energy into additional egg production.