Fleas are small wingless insects that feed as adults on the blood of birds and mammals. Most fleas are active insects moving freely over the body of their host and frequently moving from one individual host to another. Adult fleas can live one year or more. The most important disease transmitted by fleas is plague or the Black Death. Fleas usually leave the host to lay their eggs, laying them in the dirt or on the bedding or nest of their host, the eggs hatch into tiny whitish legless larvae, the larvae feed on organic debris and the faeces of adult fleas.