Egg is the beginning of insect life. After mating, depends on different species, female fireflies would lay eggs at specific place, such as between leaves of aquatic plants or mosses, wet and sheltered bark cracks, rock crevices, soil cracks, or beneath litter and soil. Number of eggs laid by one female ranges from tens to hundreds. Egg size variation across different species is great, egg diameter ranges from 0.5mm - 2.0mm (64 times in volume). Firefly eggs glow, also a warning signal. Egg stage lasts for few days to 30 days, for over-wintering cases, the egg stage lasts for several months. Rhagophathalmus would curl up its body around the eggs and emit up to 33 light spots from its body.

Larva is the feeding and glowing stage, the only task is searching for food and preventing attacks by predators. All insects bear exoskeleton, exoskeleton does not grow, to accommodate enlarging body, the old exoskeleton must be shed and replaced by a larger exoskeleton. This process is called moulting. After each moulting, body size increases, external appearance also changes. The larva hatches from the egg is called 1st instar larva, after moulting, it becomes 2nd instar larva, and so on. The last stage before pupation is called final instar larva. Depends on different species and food availability, there are usually 4-7 instars. All the known larvae are nocturnal, predate on nocturnal snails, slugs, earthworms, millipedes, or other insects. Larva excretes venom to paralyse the prey, and digestive juice to undergo external digestion. Digested food is absorbed simultaneously. Time for feeding is much longer, commonly overnight. Larva of most members of the Luciolinae in Hong Kong are not known yet.

Pupa is the last stage of growth and development. Final instar larva finds a suitable place for pupation, some species make underground soil chamber, some species build mud coccoon around the body, some species simply go into soil cracks or beneath litter to pupate. Mature final instar larva changes to pre-pupa first. Organs belonging to larval stage disappear and adult specific organs start to develop. After a few days, the exoskeleton cracks and sheds. Pupa is formed. Firefly pupa is very different from butterfly pupa which is well known to us. Butterfly pupa has appendages and wings firmly attached to the pupa body and is immobile. This is called obtect pupa. Like most other beetles, fireflies have exarate pupa. Appendages are free. Pupa of Lamprigera spp. can even walk for a long distance. Generally, all known pupae glow. For Hong Kong fireflies, pupa stage lasts for around 10 days before emerge as an adult.

Adult is the last stage of an insect's life. It does not grow. The only function of adult is mating and laying eggs. Wings are specific to adults. They are mainly for efficiently escaping from enemies, searching for mates and dispersing offsprings. Most species have their adult mouthparts degenerated, could only absorb water. Only few species would feed on other fireflies. Adult life is usually short, varying from a few days to about 10 to 20 days. Some wingless female adults could survive several weeks to months. Being a member of the ecosystem, fireflies are also preys of some predators. Fireflies being caught on spider web is most commonly seen in the wild. The fireflies being caught on spider web would keep emitting light until eaten by the spider.