The larvae feed on small particles of animal or plant debris and adult flea feces until they achieve full growth. Larval development may require as little as five days but may be extended for up to three weeks, depending on food and environmental conditions. Next, the larvae spin silken cocoons. These are hard to see because fleas incorporate nearby debris into the cocoon. The cocoon protects the developing flea from insecticides.
Fleas can stay in the cocoon for periods ranging from less than a week to more than four months.
Adult fleas emerge from their cocoons after a physical disturbance or in the presence of warm-blooded animals. This is why vacationers often return to find their homes overrun by fleas. The adult fleas remain in their cocoons when the house is quiet, emerging hungrily all at once when the family returns. The flea's ability to stay in the protective cocoon so long is one of the reasons an integrated control program is needed. A control program should be followed in the order outlined below.