The adult fleas are fully developed within 1–2 weeks but only emerge from the
cocoons after receiving a stimulus, such as the vibrations caused by movement of
the host. In vacant houses they may survive in the cocoons for up to a year. People
moving into a vacant house can cause many fleas to emerge simultaneously from
the cocoons and attack people or animals in large numbers. Under optimal
conditions the development from egg to adult takes 2–3 weeks.