Memory and the scheduling of parental care in an insect population in the wild

Animals are expected to schedule their activities so as to maximize fitness. Vertebrates achieve this using memories of previous events-what happened, where, and when¹^,²-but most studies have been lab based.³ Here, we investigate the scheduling of parental care by progressively provisioning digger wasps (Ammophila) in their natural environment, where fitness consequences are observable and we can relate behavior to its ecological context. Despite their miniature brains, females used information including all three elements of the what-where-when paradigm. Remarkably, they remember the locations of up to 9 separate nests simultaneously (where), each nest containing a single offspring. Without having to resample, females feed offspring in order of age (when), reducing the chance of starvation, and can adjust the sequence flexibly. Memory capacity might sometimes constrain performance: offspring were fed out of order when there were more of them to choose between or if the age sequence was altered following offspring deaths. Mothers delayed feeding offspring that had been given larger first food items experimentally (what), enabling them to initiate additional offspring earlier, but in this case decisions were based on resampling offspring needs directly rather than on memories of the food provided during egg-laying. Resampling could reflect ecological pressures rather than cognitive constraints: mothers relied on memory if resampling would expose offspring to parasites but resampled when risks were reduced. Progressive provisioning requires mothers to coordinate the feeding of multiple offspring and assess offspring maternity and needs during development. These skills may have preadapted some lineages for sociality.