Houseflies can transmit intestinal worms, or their eggs, and are potential vectors
of diseases such as dysentery, gastroenteritis, typhoid, cholera and tuberculosis.
They will frequent and feed indiscriminately on any liquefiable solid food, which
may equally be moist, putrefying material or food stored for human consumption.
Flies liquefy food by regurgitating digestive juices and their stomach contents on
to the food substance. This 'liquid' is then drawn up by the suctorial mouthparts
and in so doing the insects pick up pathogenic organisms, which may collect on their
bodies to be transferred on contact with other surfaces or survive passage through
the gut to be deposited as fly spots. Fly spotting, produced when the insect feeds
or defecates, results in rejection of contaminated farm produce, for example eggs,
at point of sale. Furthermore, flies are frequently the subject of complaints to
environmental health authorities, causing major problems where infestations over-spill
from breeding sites such as rubbish lips and animal houses.
The Lesser housefly makes longer flights and spends less time resting than the Common
housefly. Females of the species tend to remain near the breeding sites and only
the males migrate. For these reasons F. canicularis is less prone to transmit disease
than M. domestica, but large populations and similar feeding habits mean that this
insect, too, has a considerable potential to act as a vector of disease. It has occasionally
been implicated as a vector of intestinal or urinary myiasis.
Forty-eight hours after emergence as an adult, the female commences egg laying. During
her adult life of 1-3 months she is capable of producing 4-5 batches of 100-150 eggs.
The pearly-white cylindrical eggs, 1 mm in length, are laid in moist decaying matter
such as household refuse, compost or dung. The eggs hatch in 8-48 hours, giving the
smooth, white, legless maggot larvae. These burrow away from light, seeking an optimal
temperature of 21-32'C, and after 3 moults reach maturity at a length of 10-12mm.
In the summer larval development may be completed within a few days, but in winter
this process may take more than a month. When mature, the larvae leave the breeding
site for the cooler surrounding areas; e.g. soil. Here they develop as yellow, brown
or black pupae 6mm long. Depending upon conditions, adults emerge 3 days to 4 weeks
later. The full cycle is generally completed between one and 4 weeks, depending upon
It is clear that there is considerable potential for the development of huge populations.
Under temperate conditions as many as 12 generations of flies may breed in one season
whilst under tropical conditions even this rate of reproduction will be exceeded.
Lesser houseflies are prolific breeders in poultry manure, but will also breed in
other moist decaying matter. Egg laying commences when the female is 10 days old.
The eggs are bananashaped, 1mm in length and bear a pair of longitudinal ridges which
assist flotation in a liquid medium. The flattened, legless, greybrown maggots hatch
within 24-48 hours. Hairy protuberances on their dorsal surface are thought to aid
progression and floating in a semi-liquid medium. The newly hatched larvae frequently
wander for a time before burrowing into a suitable food. Larval development requires
a minimum period of 8 days, during which time the larva passes through 3 stages,
eventually attaining a length of 6mm. Pupation requires a drier location and lasts
for at least 10 days. Development from egg to adult emergence takes 3 weeks, although
cooler conditions prolong this period.