Direct Evidence for Cannibalistic Necrophagy as a Way of Nitrogen Recycling in Ants

Adequate nitrogen sources are indispensable for the development and reproduction of most animals. Some observations suggest that eusocial insects, such as termites or ants, can cover the protein requirements of their growing larvae by consuming the corpses of their own nestmates, a behavior known as cannibalistic necrophagy. While termites commonly utilize this food source, its occurrence in ants remains controversial and has so far been supported only by indirect observations (e.g., substantial weight loss of corpses or the presence of gnawed-out holes on the abdomen of the corpses). This behavior might be a crucial tool for survival under suboptimal conditions; however, long-standing evidence supporting its presence in ants is limited. In this study, we assessed whether cannibalistic necrophagy indeed occurs in ants by offering fluorescently marked corpses to their nestmates and subsequently detecting the signal within the digestive tracts of the living ants. Our results provide direct evidence that some ant species can use corpses, a constantly available food source, to fulfill the nitrogen requirements of the colony. This food source can have a variable share in the diet of a colony, and we argue that it is mainly utilized when food availability is scarce. By enabling the recirculation of nitrogen from deceased colony members, necrophagy may contribute to the ecological and evolutionary success of ants.