The black-winged firefly, Luciola cerata Olivier, is endemic to Taiwan and is the most common firefly on the island. Males flash spontaneously and females respond with bioluminescent flashes at fixed response delays. In order to explore the potential for sexual selection in L. cerata, we surveyed males at 12 sites in Taiwan. We measured variation in male morphological characteristics and mated males to females. Male flash behavior and mating success was quantified under a variety of experimental sex ratios in the lab. We found there are two male morphs of this species, which are distinguishable only by the morphology of the lantern. One morph has a pentagonal second light segment, while the other has a semi-oval second light segment and only produces a flash with the first lantern segment. Besides this difference in morphology, the flash patterns and mating behavior also differ between these two morphs. Males with a pentagonal segment have a faster flashing rate than those with a semi-oval segment and are considered more attractive to females in groups with male-biased sex ratios. Furthermore, females that mate with the pentagonal-segment morph demonstrate greater fecundity than those that mate with the semi-oval-segment morph.