Humans set budgets when facing an uncertain future. So do ants.

What is it about?

Imagine you are looking for a parking spot at a crowded event. You find one far from your destination. Do you decide to take it, or invest more time into hunting a better spot which may or may not exist? Making decisions under uncertainty is a problem we all face. In our study, we show that weaver ants (Oecophylla smaragdina) – much like humans – manage it by budgeting their investment into a task with an uncertain payoff. Weaver ants regularly link their own bodies together to form bridge-like structures called 'hanging chains', which they use to bridge vertical gaps along their trails. Building a chain is costly, as the ants in the structure cannot participate in other tasks. This cost increases with the size of the structure, as longer chains require a higher number of ants. The benefit of building a chain is to explore new areas, which may contain new food sources that ants can exploit. However, whether a new are contains valuable resources is unknown to the ants until the chain is complete. This makes chain-building a gamble. We tested whether ants would stop forming chains when confronted with tall gaps, where the cost of building a chain may outweigh its (unknown) benefits. Our study shows that ants - like humans - limit their investment into tasks when the outcomes are unknown.

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