Life-cycle of an adult cat flea Ctenocephalides felis. The eggs as shown here are white and oval usually measuring around 0.5mm in diameter. To hatch eggs need a relative humidity above 50%. This is usually found in the dog or cats bedding. Larva are negatively phototaxic (move away from light) and so often end up under the carpet. Three larval stages occur, taking around one to two weeks to develop to the pupal stage. It spins itself a silken cocoon and pupates. The adult is ready to emerge after 10 or so days. A stimulus is needed before the adult flea emerges. The stimulus needed is some type of vibration or load applie to the cooon, heat may also cause emergence. This behaviour can result in a sudden population of fleas in a previously empty house.