Fleas are parasites, feeding on blood. They are found on the host (dog, cat, man etc.) and drop off into cracks when they are finished feeding.
Fleas feed on blood and are attracted by the host’s carbon dioxide and body heat. In the case of humans, flea bites can be numerous because of interrupted feedings.
The Femal flea lays several hundred eggs in her lifetime. Eggs are laid loosely on the host and drop or are shaken off on to floors, carpets, bedding or other sheltered spots. Egg hatch in about 10 days and become adults in one to three months. A Flea infestations can number in the thousands.
Outdoor infestations die off, however once established inside the home, fleas are active year-round.