Fleas are small, wingless bloodsucking insects (order Siphonaptera) with a characteristic
jumping movement. They feed mainly on mammals but also on birds. Of
the 3000 species only a dozen commonly attack humans. The most important
species are the rat flea, the human flea and the cat flea (Fig. 4.6). Their bites can
cause irritation, serious discomfort and loss of blood. The rat flea is important as
a vector of bubonic plague and flea-borne typhus. Cat fleas incidentally transmit
tapeworms. The sand flea or jigger burrows into the skin of humans and may cause
infections. Fleas that bite people occur in most parts of the world.
The life cycle of fleas has four stages: egg, larva, pupa and adult (Fig. 4.7). Adult
fleas are 1–4mm long and have a flat narrow body. They are wingless with well
developed legs adapted for jumping. They vary in colour from light to dark brown.
The larvae are 4–10mm long and white; they have no legs but are very mobile.
The cocoon (pupal stage) is well camouflaged because it is sticky and soon
becomes covered with dust, sand and other fine particles.
Both female and male fleas take blood-meals. Fleas breed close to the resting
and sleeping places of the host, in dust, dirt, rubbish, cracks in floors or walls,
carpets, animal burrows and birds’ nests.
The larvae feed on organic matter such as the faeces of the host, small dead
insects and undigested blood expelled by adult fleas. At the end of the larval period
the larva spins a loose whitish cocoon within which it develops into a pupa.
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.