Three-day-old virgin females of Glossina austeni Newst. that had emerged in the laboratory in Britain from wild puparia collected in Africa or from subsequent laboratory cultures were caged with males over nine days old for 24 hours and dissected after death. Of the 5,474 flies so treated, 38 per cent. died within 14 days after mating day, whereas of the 593 found to be uninseminated, 73 per cent. died during that period, mostly within the first six days. A possible explanation of the discrepancy is that females with a poor expectation of life are unattractive to males, and this could account for the very small proportion of uninseminated flies in field collections, since such flies would tend to die before they could be captured.