In one to twelve days the eggs hatch into maggot-like larvae that feed on dirt and debris, including dried blood from adult flea droppings. After seven to fifteen days the larvae spin silken cocoons, usually covered with debris for camouflage, and become pupa. Adult fleas emerge from the cocoon in a week, or they can delay emergence as long as a year if conditions are unfavorable. Adult fleas can live for several months if conditions are right, even when unable to feed. Female fleas need a blood meal before they are able to lay eggs.
Flea bites cause local irritation, allergic reactions and secondary infection in the bite.
The ability of fleas to feed on a variety of hosts permits the transmission of diseases and tapeworms from wild animals to humans and pests. The infamous bubonic plague was transmitted from rats to humans through fleas. This is flea eggs and dried blood flakes. To monitor for fleas in the house, spread a light colored pillowcase on the floor again and place a shallow dish of water on it. Drop a couple of Alka-Seltzer tablets into the water, as the bubbles fizz they give off carbon dioxide that will attract the newly emerged fleas.