Female fleas lay eggs, usually on the host (your pet), however, the eggs are not attached to the hair and soon fall off and develop on the ground or in the pet's bed or resting place.
Flea eggs are oval, smooth, and white in color. Although they are tiny, they are visible to the naked eye if you know what to look for. They are soon lost in the surroundings. The eggs are laid by the adult flea, one egg at a time, while it is ´riding´ on your pet. Female fleas are very prolific and can lay up to 50 eggs a day.
The eggs hatch in 2 to 12 days under favorable conditions (65-80 degrees F, and at least 70% relative humidity). The flea grub or larva hatches by hacking a hole in the eggshell with a specially developed area of the mouth, usually refered to as a ´milk tooth´.
The young larvae are tiny, whitish, and legless, with bristly hairs. They are also visible to the naked eye. They are eyeless, legless and sparsely covered with hairs. Because the larva is sticky and covered in hairs, it quickly becomes coated in any form of dust or debris in its surroundings which camoflage it nicely.
Larvae tend to avoid light by burrowing down into carpeting, or hiding under pet bedding. It then feeds on food particles present in the dust and debris arround it.
Flea larvae feed on organic debris (hair, dander, and shed skin of the animal), their own cast skins, and on the feces of adult fleas. The larval stage may last from 4 to 24 days in the summertime, 21 to 200 days under less favorable conditions.
When fully grown, the larva spins a silken cocoon and enters the pupal or resting stage. Having covered itself in sticky silk it is again disguised by the dust and debris in its surroundings. Safely inside it will metamorphose into the adult flea.
Under optimal conditions, new adults are ready to emerge within 2 weeks. They develop faster at higher temperatures, but can remain in their cocoons and stay alive for up to 2 years before hatching.
The main trigger for adult fleas to emerge seems to be vibration. A room can be empty for several months, but walking across the floorboards can cause enough disturbance that a host of fleas will be rampant within minutes.
The adult cat and dog fleas emerge from the pupae, and often crawl up on blades of grass outdoors, or onto furniture, draperies or the like indoors, and wait for a host to pass. If anything in the vicinity is at the same temperature as blood, the fleas are rapidly attracted to it - you, the dog, the cat, or anything else which may be a source of food.
They jump quickly onto the new host and begin feeding. Adults of the cat flea and dog flea are long-lived; they may live for a year of more, with periodic feeding. It is only during the adult stage that the flea lives on your pet and feeds on fresh blood.
Having fed, they are then able to lay an egg. They can repeat this process up to once every half hour when at their peak, and can lay more than 300 eggs in a lifetime. These move into the surroundings and off we go again! The whole cycle in good Summer weather or efficient central heating can be comfortably less than four weeks.
Dispite popular belief, most fleas do not pass animal to animal, but stay with the host that they first attack. Most infections are picked up directly from the environment. Of course other infected animals will be contributing to the pool of new infestation by shedding eggs. Hence most animals in fact set up their own private supply of pet fleas.
Source: University of Florida Extension Service
