Effect of water and resource availability on ant feeding preferences: a field experiment on the Mediterranean ant Crematogaster scutellaris

Ants’ feeding habits are affected by individual and collective needs, which may vary among seasons. In this study, we tested the food preferences of the Mediterranean ant Crematogaster scutellaris toward sucrose and amino acid solutions at increasing concentrations, during spring and summer, by analyzing individual choices and mass recruitment in the field. Given that water may be limiting in summer, we also analyzed the role of water as a resource itself. Finally, to investigate how previous short-term availability of resources affects feeding choices, we over-supplied colonies with a continuous flux of amino acids, sucrose and water, before conducting individual tests. As for sucrose, only the most concentrated solutions were largely accepted during the spring, whereas all the solutions were equally taken during the summer. On the contrary, the average acceptance of all amino acid solutions was high only during summer and low in spring. Similar results emerged for recruitments on both nutrients. Amino acid supplementation had no effect on resource acceptance, whereas both sucrose and water supplementation affected the acceptance of all other resources. This study provides hints on the factors affecting seasonal variations in the uptake of carbohydrates and amino acids, and more importantly, clearly shows how food choice is affected by water availability, a factor frequently overlooked in the study of nutritional ecology of ants.