There are four stages of metamorphosis that a firefly goes through. It they are called Holometabolism.
Life cycle : the firefly egg is only half a millimeter in diameter. The firefly develops inside the egg. The eggs hatch about 20 days after they have been laid. A firefly larva hatches from its egg by biting through the egg covering and pushing its body out of the egg. The larvae float on the surface of a river or a stream and then they sink to the bottom where they hide under a rock looking for food. While underwater the larvae breathe through a tube-like gill on their abdomens. When a larvae molts, it bends and twists its body until its old skin splits and it wiggles out of the old skin revealing the new lighter skin underneath. When it has finished its development a larva leaves the water and moves out onto the moist soil. After its final molt the larva is transformed into a pupa. The pupa stays underground for ten days. The pupa begins moving and it bends its body until the pupal shell splits. The pupa shell splits at the back and the firefly works its way out of the shell and pushes its transparent covering down into the bottom. The firefly comes out of the pupal covering and now it is a fully developed firefly.