The distribution of Caryedon serratus, the peanut (groundnut) bruchid, on 2 Australian native plants, Cassia brewsteri and C. tomentella, was documented over 2 years. Caryedon serratus was observed across the central and northern parts of the range of C. brewsteri (latitudes 19.258–24.140°S) and at least part of the range of C. tomentella (as far as 24.427°S). Seed loss to C. serratus in these species assessed across all collection sites was 40 ± 8.0% (mean ± s.e.). Where the bruchid was detected at a given site, 72 ± 8.6% of pods on 71 ± 8.5% of trees were affected. Additional distribution points and other potential host species from previous C. serratus collections in the Australian National Insect Collection (ANIC) are reported. The combined data were used to predict a potential range for the bruchid across the dry tropics of Australia. No reports of migration to cultivated or stored peanut (Arachis hypogaea) in Australia were located. Further investigation of the potential impact of this bruchid on the Australian peanut industry is recommended. A potentially beneficial aspect of C. serratus establishment may be the biological control of Acacia nilotica (prickly acacia) in Australia.