Why fruit fly sperm are giant

The fruit fly Drosophila bifurca is only a few millimeters in size but produces almost six centimeters long sperm. Researchers provide the first explanation for the evolution of such giant sperm. Larger sperm are able to displace their smaller competitors from the female reproductive tract — a competitive advantage in fertilizing the eggs. Female promiscuity increases the fertilization success by larger males, which can produce more of the longer sperm.