How a lack of choice can force ants to climb up waxy plant stems

The aim of this study was to analyse the ability of generalist ants to climb waxy stems and to understand whether the avoidance of such stems is solely based on their reduced ability to adhere to these surfaces. We performed observations of the locomotory behaviour and recorded the traversed distances of Lasius niger ants on flower stems of three plant species covered with epicuticular wax crystals: Anethum graveolens, Dahlia pinnata, and Tagetes patula. Using conventional and cryo-scanning electron microscopy, the surface micromorphology of plant stems and structure of ant attachment organs were examined. The present study demonstrates that the reason ants do not climb wax-covered stems is not because they are incapable of walking on such vertical surfaces, as previously assumed, but rather because they have a choice of other substrates. Presumably, additional locomotory efforts are needed to master climbing on greasy stems, and ants need a certain time to adapt to a new quality of the stem surface, and after this period, they can walk on these waxy stems.