The way fleas reproduce depends on their species and environmental conditions, states "Flea Control: How to Get Rid of Fleas Naturally." For example, the water flea reproduces asexually under normal conditions. These fleas only produce females until abnormal conditions, such as overcrowding or a limited food supply, cause them to asexually produce only males. The male fleas then mate with the females to continue reproduction until conditions change again.
Fleas lay a cluster of up to 20 eggs or more, but this can only occur if a flea has fed on blood after emerging from its cocoon. If a flea is unable to feed, it dies without reproducing. After the eggs are laid, they hatch into worm-like larvae in approximately 12 days.The larval period lasts through three separate stages, with molting occurring after each stage is complete. The larval stage lasts approximately 2 weeks.
After the third larval stage, the fleas spin cocoons and become pupae. After this stage, they emerge as adult fleas in approximately a week if food is plentiful. If no food is available, pupae can stay inside their cocoons for up to a year until food is once again available. Pupae use vibrations, sound, carbon dioxide and heat to determine whether a food source is nearby.