Harvester ants, a non-generic name, are any of the species or genera of ants that collect seeds (called seed predation), which are stored in the nest in communal chambers called granaries. Seed harvesting by some desert ants is an adaptation to the lack of typical ant resources such as prey or honeydew from homopterans.
Harvester ants foraging in hot, dry conditions lose water, but obtain water from metabolizing fats in the seeds that they eat. Positive feedback on foraging activity, from returning foragers with food, allows the colony to regulate its foraging activity according to the current costs of desiccation and the benefits based on current food availability.
In many harvester ant species, foraging behavior is influenced by the weather. Both humidity and food availability are affected by day to day changes in weather conditions. Food is distributed by wind and flooding and rain uncovers seeds in the top layer of the soil. In Pogonomyrmex barbatus, daily changes in conditions such as humidity and food availability produce strong daily trends in the foraging activity of all colonies.
Colonies may vary in the relation between humidity and foraging activity. Colonies differ consistently from year to year in how often they forage at all and most colonies forage on days with high humidity and high food availability, such as those just after a rain when flooding has exposed a layer of seeds in the soil. Few colonies forage on very dry days. Colonies also differ in how likely they are to adjust the rate of outgoing foragers to the rate of forager return. While all colonies tend to adjust outgoing foraging rate closely when conditions are good, only some colonies do so in poor conditions.