Nabidomiris Poppius, 1914 is an African plant bug genus with three described species. Here we describe as new a fourth, Nabidomiris natalensis sp. nov. from KwaZulu-Natal (South Africa), and compare it to the other known species. Because male genitalia are important for species delimitation, and it has never been documented for any of the species of Nabidomiris, we describe for the first time the male genitalia of N. clypealis Poppius, 1914, N. longipennis Odhiambo, 1958, and N. giloicus Linnavuori, 1975. We provide a key to separate all species, and new country records for the previously described species. Nabidomiris clypealis is recorded for the first time from the Democratic Republic of the Congo and South Africa, N. giloicus from Cameroon, and N. longipennis from Tanzania.