Flea eggs are about O.5mm long, oval, pearlywhite in colour and laid indiscriminately
in the fur or feathers of the host or in its nest or bedding. They do not adhere
to the host but readily fall from the animal, are shaken or scratched off. The same
applies to the dark coloured faeces of the adult fleas thus creating the black and
white - salt and pepper effect associated with flea infestations. Four to eight eggs
are laid after each blood meal and a single female may produce 800-1000 eggs during
her lifetime, which may be as long as two years.
The eggs hatch in about one week to give white, threadlike, legless larvae 1.5mm
long. These are distinguished by an identifiable, usually brownish head without eyes;
jaws adapted for biting; three thoracic segments and 10 abdominal segments all equipped
with bristles; and peg-like processes on the terminal abdominal segment. The larvae
thrive in dark, humid places such as animal bedding and carpet fluff, and feed on
organic debris and adult flea excrement. The latter forms a valuable part of the
diet as a source of blood, which some larvae, while not attacking the host, require
for their development. Larvae may also be predacious, living on small and weak arthropods.
Cats' bedding may support a flea population of 8000 immature and 2000 adult forms.
A typical flea infestation may be composed of adults 5%, larvae 35%, pupae 10% and
After 2-3 weeks, by which time they will have moulted twice and be about 5mm long,
the larvae spin silken cocoons, incorporating debris, in which to pupate. The cocooned
larvae then moult within three days to give the pupae which are initially creamy-white
but change to dark brown as they mature to become adults. This phase is the quiescent
stage and the flea may overwinter in this state. The adult flea will then be stimulated
to emerge by the vibrations set up by a passing host. This explains the occasional
mass attacks which take place in deserted premises.The development cycle from egg
to adult is normally completed in 4 weeks but at low temperatures will take much
Fleas can be vectors of disease or may transmit parasitic worms. The most serious
infection which they can spread is bubonic plague, transmitted to man by rodent fleas
(Xenopsylla cheopis) which carry the causative bacillus from infected rats. In the
past rodent fleas have been responsible for serious epidemics of the disease, notably
the Black Death in Europe and Asia in the 14th to 17th centuries. Rodent fleas may
also carry murine typhus and, because of their readiness to attack humans as well
as rats, are probably the major flea vector of disease. The Dog flea is an intermediate
host of the Dog tapeworm (Dipylidium caninum), whose vertebrate host is usually the
dog (occasionally the cat) but which can sometimes be transmitted to man.
In Europe fleas are not generally responsible for the transmission of disease. However,
they are still objectionable because of the bites they inflict and the deep-rooted
social stigma attached to humans with flea infestations. Occasionally psychological
problems arise with the induction of delusory parasitosis, in which the victim imagines
he is infested with ectoparasites.
Flea bites are identified as a tiny dark red spot surrounded by a reddened area.
The bite persists for one or two days and is intensely irritating. First bites are
not generally liable to cause serious reactions, but they may lead to hypersensitivity.
Reactions are usually delayed following regular biting over a long period; there
will then follow a period when reactions are immediate. The cycle then repeats until
a state of non-reactivity - immunity - is achieved.