Fleas are associated with dogs and cats. They require warm temperatures and relativity high humidity to develop, which explains why they typically aren't a problem until late summer or fall, but can be a problem at any time of the year under the right conditions. There are four stages in the flea life cycle; the egg, larvae, pupa, and adult. It has been estimated that in a flea infestation, the adults (What is being seen) comprise only 10% of the entire population. The adults obtain a blood meal from a dog, cat, or human, and then lay eggs which are deposited(by the animal shaking) in carpeting, upholstered furniture, the bottom of draperies, etc. The eggs hatch into larvae which feed on small particles of organic matter. The larva then builds a cocoon and pupates, during which time it turns into an adult. The flea can remain in the pupal stage for months until warmth and/or vibration cause it to hatch out. This explains why people who go on vacation with their pets or board them will come home and be covered with fleas in just a few minutes.