First report of leaf swallowing and parasite expulsion in an Asian small ape

Leaf swallowing behaviour, known as a form of self-medication for the control of nematode and tapeworm infection, occurs widely in all the African great apes. It is also reported to occur in a similar context across a wide array of other animal taxa including, domestic dogs, wolves, brown bears and civets. Despite long-term research on Asian great and small apes, this is the first report of leaf swallowing in an Asian species, the white-handed gibbon ( Hylobates lar ) in Khao Yai National Park, central Thailand. We present the first evidence of leaf swallowing ( Gironniera nervosa Planch CANNABACEA) behaviour (n = 5 cases) and parasite (Streptopharagus pigmentatus) expulsion (n = 4 cases), recorded during 4,300 h of direct animal observations during 2 distinct research projects. We recovered 4 – 18 rough, hairy and hispid surfaced leaves from each sample, undigested and folded, from the freshly evacuated faeces of 5 different individuals (2 males, 3 females, 5 ∼ 34+ years old) living in 3 different social groups. Based on close inspection of the leaves, as observed in chimpanzees, it was clear that leaves were taken into the mouth, one at a time, folded and detached from the stem with the teeth before swallowing them whole. All instances occurred during the rainy season, the time when nematode worms were also found in the faeces. These striking similarities in the details of leaf swallowing between white-handed gibbons and African great apes, and other animal species, suggest a similar anti-parasitic function