Leaf-swallowing by chimpanzees: A behavioral adaptation for the control of strongyle nematode infections

Michael A. Huffman, Jonathan E. Page, Michael V.K. Sukhdeo, Shunji Gotoh, Mohamedi S. Kalunde, Thushara Chandrasiri, G. H.Neil Towers

Research output: Contribution to journalReview articlepeer-review

48 Scopus citations


Swallowing whole leaves by chimpanzees and other African apes has been hypothesized to have an antiparasitic or medicinal function, but detailed studies demonstrating this were lacking. We correlate for the first time quantifiable measures of the health of chimpanzees with observations of leaf- swallowing in Mahale Mountains National Park, Tanzania. We obtained a total of 27 cases involving the use of Aspilia mossambicensis (63%), Lippia plicata (7%), Hibiscus sp. (15%), Trema orientalis (4%), and Aneilema aequinoctiale (11%), 15 cases by direct observation of 12 individuals of the Mahale M group. At the time of use, we noted behavioral symptoms of illness in the 8 closely observed cases, and detected single or multiple parasitic infections (Strongyloides fulleborni, Trichuris trichiura, Oesophagostomum stephanostomum) in 10 of the 12 individuals. There is a significant relationship between the presence of whole leaves (range, 1-51) and worms of adult O. stephanostomum (range, 2-21) in the dung. HPLC analysis of leaf samples collected after use showed that thiarubrine A, a compound proposed to act as a potent nematocide in swallowing Aspilia spp., was not present in leaves of A. mossambicensis or the three other species analyzed. Alternative nematocidal or egg-laying inhibition activity was not evident. Worms of O. stephanostomum were recovered live and motile from chimpanzee dung, trapped within the folded leaves and attached to leaf surfaces by trichomes, though some were moving freely within the fecal matter, suggesting that the physical properties of leaves may contribute to the expulsion of parasites. We review previous hypotheses concerning leaf-swallowing and propose an alternative hypothesis based on physical action.

Original languageEnglish (US)
Pages (from-to)475-503
Number of pages29
JournalInternational Journal of Primatology
Issue number4
StatePublished - Aug 1996

All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics
  • Animal Science and Zoology


  • Oesophagostomum stephanostomum
  • antiparasite behavior
  • chimpanzees
  • physical expulsion
  • trichomes


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