Bottle fly trap - Kenya
Practical Action
Attracting Flies
Flies have developed a close relationship with human habitation over many centuries, to the benefit
of the fly populations. This association has resulted in the deaths of thousands of people, due to the
ability of this humble insect to transmit disease. Non-biting flies have adapted to the different niches
available within human populations, which permit them to feed, grow and reproduce. Their feeding
and breeding habits enable these flies to be effective mechanical vectors of disease to humans. Flies
are often responsible for the contamination and spoilage of foodstuffs, annoyance, mechanical
transmission of disease-causing pathogens, and invasion of living tissues (myiasis).
Non-biting flies are often associated with domestic dwellings, especially throughout the warmer
months when flies breed prolifically. Flies are equipped with special sensory cells on their antennae
and feet, which enable them to locate suitable food and egg laying sites. These sensory cells aid in
detecting substances such as ammonia, carbon dioxide and other strong compounds that are emitted
from decomposing organic materials, such as carrion and faeces. Being attracted to these locations
means that the flies are laden with bacteria on their mouthparts, body hairs and the sticky pads of
their feet, as well as in their stomachs (where the bacteria rapidly multiply), faeces and vomitus.
Contact with any foodstuffs, or feeding, which often involves vomiting and defecating, will
contaminate food, preparation surfaces and utensils with potentially disease-causing organisms. Eggs
or young larvae may also be deposited if the material is deemed suitable for egg-laying by the fly.
Flies can also be strongly attracted to uncovered, malodorous wounds, body openings, open sores or
damaged skin. Some species will deposit their eggs or larvae on the site if the circumstances are
suitable. This can result in myiasis, where young maggots feed on healthy or diseased tissue to
complete their growth cycle.
In Maasai communities, common fly-borne diseases include trachoma and diarrhoea. Trachoma is an
eye infection caused by the bacterium Chlamydia trachomatis. Trachoma is highly infectious, and in
some areas of the world the infection rate in children is 100 per cent. About 400 million people are
affected by trachoma in parts of Africa and Asia. It is transmitted when eyes come into contact with
infected fingers, flies or contaminated materials. It tends to occur between people living in poor
social conditions. Symptoms include scarring of the inner lining of the upper eyelids, which causes
the lids to curl inwards (known as entropion) so that the lashes rub against and scar the very front of
the eye (the cornea). This opens the way to further infection, which can result in permanent blindness
if not treated.
Diarrhoea is the passing of
frequent, watery stools.
People with diarrhoea may
also have cramps in their
stomach, feel sick (nausea),
feel feverish (high
temperature) and lose their
appetite. Diarrhoea is a
symptom, and can be acute
(short term) or chronic (if it
continues for more than two
weeks).
Acute diarrhoea is usually
caused by a viral infection
or a bacterial infection and
affects almost everyone
Livestock market Photo: Practical Action / Simon Ekless
from time to time. It
usually clears up in a
couple of days and is not serious. However, it can be serious in babies and the frail and elderly,
because of the risk of dehydration.
2