Under-differentiating classificatory systems pose methodological problems for cultural domain analysis in particular, and ethnobiology in general. Our analysis suggests the Roviana people from the Western Solomon Islands do not have a word for the category “insects” and their classification scheme for little terrestrial animals is rather generic and undifferentiated in comparison to scientific taxonomy. In most cases the accuracy of cultural domain methods depends on the identification of homonymous categories between local and Western classificatory systems. This, as the case study illustrates, is not always possible due to under-differentiation, and analytical alternatives need to be considered for building and understanding indigenous biological classificatory systems.