The canopies in tropical rainforests harbor species-rich arboreal ant assemblages. However, few studies have examined how these arboreal ants affect the web of interspecific interactions among organisms there. This study examined effects of a typical arboreal ant species, Crematogaster difformis, which forms myrmecophytic symbiosis with epiphytic ferns, on the activities of insect herbivores on canopy trees and on the growth of lianas clinging to canopy trees, by conducting field observations and experiments.

Herbivory damage on new leaves on branches from which any of C. difformis were excluded experimentally was significantly higher than that on new leaves on control branches where the ants formed their territories. Lianas that were experimentally placed inside the territories of C. difformis in the canopy were attacked and removed by the ant workers. For the emergent tree species from which nest of C. difformis had been recorded, the rate at which at least one liana reached the crown of an emergent tree was significantly lower on emergent trees with either of the ferns than on those without any of the ferns.

These results suggest that C. difformis greatly regulates both the herbivory damage and the growth of lianas clinging to the crowns on several species of emergent tree.