Fleas undergo complete metamorphosis — egg, larva, pupa, and adult four stages.
The entire life cycle can be completed in 2–3 weeks (under conditions of 25–30 °C and 70–85% humidity).
Adults account for only about 5% of the total flea population — every flea you see on your pet corresponds to about 20 immature stages in the environment.
Adults live from several weeks to months; a female flea lays 20–50 eggs per day and can lay several thousand eggs in her lifetime.
The eggs are white, about 0.
5 mm, with a smooth surface that does not stick to pet fur — most eggs fall off into carpets and pet bedding.
The larvae are maggot-like, avoid light, and burrow deep into carpet fibers, feeding on adult flea feces (flea dirt, containing undigested blood).
The pupa can sense environmental signals to determine if a host is nearby and can remain in standby within the cocoon for months — this is why a long-vacant house may suddenly have a flea outbreak when new occupants move in.
Breaking the flea life cycle requires simultaneous treatment of both the pet and the environment.