Note the numerous black ants on the twig that appear to be collecting the flaking bark from the twig. The top blue arrow points to a waxy gland at the base of the leaf which provides ant food. The bottom blue arrow points to the base of an ant house (domatia) which appears to be under construction.
In this article we hypothesize that the flaking bark characteristic of Ficus uniglandulosa twigs has evolved to provide building materials for ants to construct domatia on the underside of the leaves. The purpose behind providing housing and food for ants is to “pay” the mercenary army of ants to stay on the plant to provide a defense against leaf eating insects.
A closely related Bornean fig Ficus scaberrrima is also known to have a mutualistic relationship with ants by developing slits for ants to enter the hollow twigs which can then be used by ants for housing,
According to Maschwitz (1994) who made a study 37 different Bornean fig species with hollow twigs, in a Ficus uniglandulosa twig she examined, out of 7 internodes of a slightly swollen hollow branch one had a closed slit similar to the slits she found in Ficus scaberrima.