Behaviour 2019
Stilt-legged flies (Diptera: Micropezidae) kick ants away from food sources
Fernando G. Soley. Organization for Tropical Studies & Escuela de Biología, Universidad de Costa Rica, San Pedro, San José, Costa Rica

When foraging, social insects commonly have an advantage because groups of workers can outperform solitary individuals. The ability to quickly recruit nestmates is one of the reasons behind the ecological success of ants. Recruitment allows ants to outcompete rivals by quickly exploiting a resource or by direct dominance granted by the sheer number of colony members attracted to the resource. Many species of ants forage above the ground and feed on honeydew excreted by homopteran insects. Ptilosphen viriolatus is a micropezid fly that commonly forages at these sites. When encountering ants, P. viriolatus either avoids them or removes them using powerful leg thrusts (i.e., kicks). In experiments, kicks delivered by the flies were highly efficient in removing ants from the leaves. Two results suggest this behavior functions to prevent ant recruitment: i) flies were more likely to kick ants early in the recruitment process, and ii) kicking slowed down or prevented recruitment, allowing the fly to consume the resource in the meantime. This behavior may be an adaptation that allows P. viriolatus to turn the scales and access food resources that would otherwise be unavailable.