Male L. vigilax are shown to displace (remove and reposition) sperm from previous males stored in the bursa copulalrix of females they mate with. Females carry sperm from two or more matings in a large bursa copulatrix. Spermathecae do not exist in this lestid. The magnitude of sperm displacement, while difficult to estimate because of changes in sperm density, appears to be on the order of 50%. Displacement occurs primarily from the central region of the bursa adjacent to the vagina. The last male to mate appears to gain a fertilization advantage by not only displacing the sperm of previous males, but also by placing his sperm closest to the area where fertilization occurs. Male L. vigilax penis morphology used for sperm displacement is less complex than that used by coenagrionid and calopterygids so far studied.