Ants adjust their tool use strategy in response to foraging risk

Authors: ZHOU, AIMING - Huazhong Agricultural University; Du, Yuzhe - Cathy; Chen, Jian

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2020
Publication Date: 10/7/2020
Citation: Zhou, A., Du, Y., Chen, J. 2020. Ants adjust their tool use strategy in response to foraging risk. Functional Ecology. 00:1-12. https://doi.org/10.1111/1365-2435.13671.
DOI: https://doi.org/10.1111/1365-2435.13671

Interpretive Summary: The ability to make and use tools has been reported in many animals including ants. Chimpanzee and certain birds have demonstrated their remarkable skills in making and using tools. For vertebrates, tool use has been considered as a possible indicator of cognitive sophistication and a driving force in the evolution of intelligence. However, tool use in invertebrates such insects was previously thought to be hard-wired and not flexible. In this study, we reported an exceptional tool making skill and tool use flexibility in black imported fire ants. While foraging on sugar water solution in a container, when the risk of drowning was enforced, instead of foraging directly over the container, black imported fire ants change their approaches to build a sand structure that can function as a syphon. The structure quickly syphoned out the sugar water, so ants can collect the liquid food outside the container. This syphon structure not only prevent ants from being drowned, but also facilitate the collection of the liquid food, likely by providing larger operational space. Our study is the first to demonstrate such remarkable creativity and flexibility of tool use in ants.

Technical Abstract: 1. Ants are among a few invertebrates that can use certain tools. For example, some ants can use debris and soil grains to transport liquid food. Although there has been evidence showing that ants can select the most efficient tools in transporting liquid food, little is known about their flexibility in using a specific tool under environmental pressure. 2. Black imported fire ants, Solenopsis richteri Forel, can use sands as a tool for foraging. We hypothesized that S. richteri can adjust their strategy of tool use in response to various foraging risks. The hypothesis was tested by studying their sand use behavior in response to sugar water with different drowning risks. 3. The results support our hypothesis. S. richteri indeed adjusted their strategy of tool use in response to increased drowning risks. Due to their hydrophobic cuticle, S. richteri can float on water surface to forage directly with the minimal risk of drowning. However, when the drowning risk was elevated by reducing the surface tension of sugar water in a food container by the addition of surfactant, ants used sands to build a structure that could effectively function as a syphon instead of directly foraging inside the container. This sand structure could draw sugar water out of the container then to be collected by the ants, which not only reduced the drowning risk of ants, but also provided a larger operational space for their collection of sugar water. 4. This study demonstrates that ants can not only recognize the increase in foraging risks, but also make corresponding adjustments to their strategy by using a specific tool. Our results also suggest that social insects can be highly flexible in their tool use in response to ecological challenges.