The Elements of Evolution (43-13) Harvester Ants

 Harvester Ants

Collective behavior arising from interactions among societal members can determine a population’s success.

Common in the southwest United States, red harvester ants reside in the desert. Their water intake comes mostly from metabolizing the fats in the seeds they eat.

Each harvester ant colony is founded by a single queen. 5 years into her reign colony population may stabilize at 10,000. Offspring colonies are founded by newly mated gynes: females destined by caste to become queens.

A colony’s foraging activity varies daily, depending upon local food supply and weather. Foragers interact, creating a feedback loop of communication that results in a community decision as to a day’s level of effort.

Ants lose water when foraging. Sometimes it can be so hot and dry that a foraging ant can desiccate to death.

The more successful colonies forage when conditions permit, forgoing foraging on scorching days. Restraint does not compromise a colony’s prospects of survival over its queen’s 25-year lifespan. Colonies that selectively fail to forage do as well as those that brave the hot sands.

Foraging theory for social insects generally presumes that the more food collected, the better for reproductive success. Harvester ants show that this is not necessarily so.

Harvester ant colonies store seeds for many months. Conserving water in various ways is a ubiquitous adaptation for desert animals, as red harvester ants demonstrate by intelligently managing their activity to optimize outcomes.

A daughter harvester ant founds her new colony far from her birthplace. There is no communication between mother and daughter colonies. No cultural transmission occurs. Yet the daughter knows what her mother did and how it fared. The tendency to forgo foraging is passed from queen to gyne epigenetically: a precious precocious knowledge. (Molecules coating DNA can’t literally impart information. The use of epigenetics here is loose: referring to molecular artifacts that signify a mind-energy complex.) Thus, each colony takes its innate cue for best foraging practices from former founders.