Blue bottle flies have the complete cycle of egg, larva, pupa, and adult.
Development usually takes around 2 weeks.
A female blue bottle fly lays her eggs where she feeds, usually in decaying meat, garbage, or feces.
Pale whitish larvae, commonly called maggots, soon hatch from the eggs and immediately begin feeding on carcasses of dead animals and on the decomposing matter where they were hatched.
After a few days of feeding, they are fully grown.
At that time they crawl away to a drier place where they burrow into soil or similar matter and pupate into tough brown cocoons.
The pupal stage is the longest stage of the development cycle.
 
After two or three weeks, the adults emerge from the pupal stage to mate, beginning the cycle again.
During cold weather, pupae and adults can hibernate until higher temperatures revive them.
Blue bottle flies have the complete cycle of egg, larva, pupa, and adult. Development usually takes around 2 weeks. A female blue bottle fly lays her eggs where she feeds, usually in decaying meat, garbage, or feces. Pale whitish larvae, commonly called maggots, soon hatch from the eggs and immediately begin feeding on carcasses of dead animals and on the decomposing matter where they were hatched. After a few days of feeding, they are fully grown. At that time they crawl away to a drier place where they burrow into soil or similar matter and pupate into tough brown cocoons. The pupal stage is the longest stage of the development cycle.  
After two or three weeks, the adults emerge from the pupal stage to mate, beginning the cycle again. During cold weather, pupae and adults can hibernate until higher temperatures revive them.
Calliphora vomitoria