Small hive beetles (SHB), Aethina tumida, are parasites and scavengers of honey bee colonies and have become an invasive species with established populations in the USA and in Australia (Neumann and Ellis, 2008). They seem to have a female-biased adult sex ratio in the USA (Ellis et al., 2002a) and in Africa (Schmolke, 1974), but the latter report is based on only two infected hives in Zimbabwe. Otherwise, SHB sex ratios have only been analysed during laboratory rearing, also suggesting a bias towards females (Neumann et al., 2001a; Ellis et al., 2002b; Mürrle and Neumann, 2004). We here provide the first systematic analyses of adult SHB sex ratios in Australian field populations and re-address South Africa. Since the two sexes of the SHB seem to differ in flight activity (Elzen et al., 2000), we also compared the sex ratios of newly infested colonies with those that had been infested for longer.