The total lifespan of a lightning bug is anywhere from one to two years. However, the bulk of that lifespan is spent underground in the larval phase. Adult lightning bugs have very short life spans, averaging just two months in the wild.
One species of lightning bugs, Photinus pyralis, has an adult lifespan as short as five days. The maximum these bugs live once they achieve their adult form is one month. Adult lightning bugs of all species are entirely focused on mating. In some species, the adults do not even eat. Once an adult has mated and eggs have been produced, the adult dies. Young lightning bugs live in the soil and actively prey on slugs and insects until they pupate either the summer after or two summers after they were hatched. Pupating usually takes 10 days to several weeks before the adult form is achieved.