Two brain chemicals that ancient organisms first used to regulate hunger and feeding also determine whether ants nurse larvae or abandon that duty to forage, according to a study published in Nature.
The research, conducted on the clonal raider ant, Ooceraea biroi, identifies neuropeptide F (NPF) and allatostatin A (AstA) as key switches controlling brood-care behavior. NPF increases the amount of time ants spend tending to larvae, while AstA has the opposite effect, the study found.
Clonal raider ants provided an ideal system for this research because, within a colony, all ants are genetically identical. This let researchers isolate how age and internal chemistry — rather than genetic differences — drive behavior.
Like many social insects, young worker ants in these colonies primarily care for larvae inside the nest, then shift toward foraging outside the nest as they age. In the study, ants that were 12 days old spent, on average, more than twice as much time nursing larvae as ants that were four months old, and less than half as much time foraging.
To probe the biology behind this shift, researchers designed a behavioral test in which individual ants were placed with a single larva in a narrow corridor and filmed for five hours. The ants displayed a consistent two-phase pattern: an initial period of near-constant physical contact with the larva, followed by a second phase in which they periodically left the larva to move around. Young ants consistently spent more time in close contact with larvae than old ants did, mirroring patterns seen in full colonies.
Notably, when ants were given food instead of a larva, they behaved differently, and the age-related differences in behavior disappeared — reinforcing that the observed contact behavior was specific to brood care rather than generic activity.
A screening approach
To find the molecular drivers of this behavior, the researchers first cataloged the ant's neuropeptide-producing genes, identifying 42 precursor genes encoding 70 distinct neuropeptides. They synthesized 61 of these peptides — excluding nine that were too large and structurally complex to produce — and tested each one by soaking ants in peptide solutions before running them through the larva-contact assay.
This initial screen flagged 24 candidate neuropeptides that appeared to influence how much time ants spent with larvae. Researchers ranked these candidates by statistical significance and effect size to narrow the field, ultimately zeroing in on NPF and AstA through further functional testing.
The study also found that natural levels of NPF and AstA in the ant brain change as the insects age, suggesting these shifts help explain the transition from brood care to foraging over an ant's lifetime. In addition, both peptides remained sensitive to the ants' nutritional state, and that nutritional state affected brood-care behavior accordingly — echoing how these peptides function in solitary, non-social species.
The findings suggest that evolution repurposed molecular machinery originally used to regulate feeding to enable cooperative brood care and age-based division of labor within insect societies.