Foraging is prioritized over nestmate rescue in desert ants and pupae are rescued more than adults

Social animals, and ants, in particular, exhibit a range of cooperative behaviors. One such behavior is the rescue of group members, which cannot return to the nest by themselves. However, if several group members need to be rescued, how do ants prioritize whom to save first? Furthermore, when food is offered in parallel, do ants prioritize feeding over rescuing? We studied the rescue behavior of the desert ant Cataglyphis niger. Workers invest more time in rescuing pupae than adult workers, perhaps because the value of brood is higher than that of older workers serving as foragers. Specific rescue behaviors, pulling the trapped individual or digging around it, differed when directed toward adults or pupae: rescuing workers more often pulled pupae whereas they dug more around trapped adults. Rescuing workers did not prioritize living individuals over dead ones or intact workers over injured ones indicating that trapped individuals were recognized chemically rather than by their morphology or behavior. Finally, workers prioritized foraging over rescuing, perhaps because fewer workers specialize in rescue behavior than in foraging. Our analysis indeed revealed that fewer workers both foraged and rescued trapped workers than expected by chance. In conclusion, ants that rescue others exhibit a complex set of behaviors, with varying attention and specific behaviors targeted at different individuals, perhaps according to the colony's needs. Our study is important for emphasizing a relatively neglected aspect of sociality (rescue of group members) and demonstrates that the attentions of rescues differ based on the trapped nestmate's life stage.