In the late 1980s, the parks service in the United States were concerned about the deterioration of the stonework on the Lincoln Memorial. So they asked the maintenance staff why the stone was decaying.
The crew explained that they used high-power sprays every fortnight to clean the masonry. The water penetrated cracks and joins, weakening the stone. But they needed to spray to get rid of the large volume of bird droppings. So they erected bird nets. These scarcely worked, and were unpopular with tourists, so the parks service called in the maintenance workers again and asked, ‘Why are there so many birds?’
‘The birds come to feed on the spiders,’ they said. ‘And the spiders are there to eat the midges.’ After dark, midges covered the memorial. The spiders came to eat the midges, and the birds came to eat the spiders. So the executives tried insecticides. But this also proved ineffective: the bugs came back. So the committee finally asked one more question. Why are there so many midges in the first place?
Because the building is floodlit, they were told.
In the end they tested turning the lights on later in the evening — after sunset, not before — and also turned them off earlier, following a suggestion from Donald Messersmith, an entomologist. On evenings when they tested this approach, midge numbers fell by 85 per cent; everything worked as predicted. Once you had implemented this idea, not only would midges from the Potomac stop splatting against the white stone, but the spiders, birds and bird droppings would be reduced.
It is a wonderful story, and has entered folklore in a philosophy called ‘the five whys’. The idea is that you should always go on asking ‘why’ in order to get to the root cause of a problem rather than the proximate cause.
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