Fleas have the same life cycle as butterflies, if we understand that we can help keep our pets flea free as much as possible. Flea eggs are found wherever animals with adult fleas go. Eggs can be sterilized with certain products that are called insect growth regulators and these are found in area treatment sprays as well as some spot-on products that are applied to the skin of cats and dogs.
Eggs develop into larvae (like the catepiller stage of the butterfly) and can move a small amount of distance, eating debris and interesting things like tapeworm eggs. Yum. The larval stage is also affected by insect growth regulators. Larvae can be found anywhere a cat or dog has been (like under furniture, on couches and beds, etc.) but are very tiny and difficult to see with the naked eye.

Larvae spin cocoons which are called pupa and these are very resistant to any chemicals, as well as drying or other environmental impacts.  They just stay in a state of suspended animation until conditions are best for the little flea to survive hatching out.  Triggers for hatching include increased temperature, increased carbon dioxide, and vibration.  So, when a little furred creature walks over, exhaling, it becomes the perfect target.  The little flea pops out of the cocoon and jumps up, grabbing a ride on the pet where it will suck blood for enough energy to mate and start the whole life cycle over.

Flea bites can cause disease in those animals that are allergic to flea saliva.  Fleas may also carry organisms that can cause other diseases, in addition to removing blood from your pet!  While some may wish to avoid using chemicals to prevent flea survival, the result may be chronic exposure to blood sucking parasites that cause misery and suffering for dogs and cats.