IN AFRICA’s Rift Valley, there can be up to 32 000 flies in any given home on
a given day—too many for swatting, and more than enough to spread disease.
But a bit of low-tech fiddling with a couple of old plastic pop bottles and some
animal dung has led to the development of an effective fly trap that is helping
control the world’s second leading cause of blindness.
About 14 million people worldwide suffer from trachoma, a bacterial infection
that is spread in part by flies and inflames the eye, filling it with sticky
mucus. Over years, multiple infections tighten the rim of the upper eyelid,
forcing it to curl in on itself and prod the eye with its own lashes. This scars
the cornea, turning it white, until the sufferer can no longer see. Trachoma can
be helped by antibiotic medicines or surgery, but a cheaper, simpler option is
prevention at source: through effective fly control.
David Morley, a retired specialist in tropical child health at Great Ormond
Street Hospital in London, based his fly trap
(see Diagram) on the observation
that flies fly upward towards light after feeding. A lower bottle, plastered
with mud, is filled with an alluring mix of goat droppings and cow urine. After
the insects have gorged themselves, they fly up a plastic tube and into a clear
bottle above, where they die of exhaustion and exposure to UV light.
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During a year-long trial run in 300 homes belonging to Masai people in Kenya,
Morley’s bottles cut the fly population by 40 per cent, and the incidence of
trachoma went down by about 36 per cent.
The traps’ biggest advantage is that they’re basically free and very simple
to produce. In fact, says Morley, the kids have been making the traps in school:
“The teacher made it part of the homework.”