I smell where you walked – how chemical cues influence movement decisions in ants

7 June 2016

Wüst, Miriam; Menzel, Florian

Interactions between animals are not restricted to direct encounters. Frequently, individuals detect the proximity of others through cues unintentionally left by others, such as prey species assessing predation risk based on indirect predator cues. However, while the importance of indirect cues in predator-prey interactions has been intensely studied, their role in interactions among competitors, and their consequences for community structure, are little known to date. Ant communities are usually structured by aggressive interactions between competing species. Responding to cues of others should be useful to avoid competitors or discover food sources. In ants and other insects, such cues include chemical footprints, which they leave while walking.
Here, we investigated how different ant species respond to footprints of others. Ant colonies were confronted with footprints of other colonies or species, and the workers chose between cue-bearing and cue-free areas. Moreover, we determined the chemical composition of footprints, and compared the absolute quantities of footprint and cuticular hydrocarbons.
Ants of the species Lasius niger avoided footprints of non-nestmate conspecifics, and tended to avoid footprints of two other species. We suggest that they avoided encounters with competitors to reduce costly fights. In contrast, three other ant species approached allospecific footprints, which may represent eavesdropping to find resources discovered by others. Three of the four ant species responded differently to nestmates and non-nestmate footprints either through footprint-following or antennation behavior. The chemical composition of footprints was species-specific and largely congruent to cuticular hydrocarbons. Footprint quantities left by single workers represented 1/170 to 1/64 of the quantity of their cuticular hydrocarbons.
We showed that chemical footprints represent an important cue for behavioral decisions in ants. The ability to identify and respond to chemical footprints may represent an important strategy for insects to cope with competing species or colonies in their habitat.