Why are flies attracted to light?

The jury is still out on the tragically one-sided relationship between flies and front-porch light bulbs, but several interesting explanations abound.
One theory suggests that moths are attracted to light because of their migratory nature. Flies regularly travel long distances guided by starlight and the moon. Hence, a light bulb may act as a proxy moon.

USA Today seconds this argument, claiming that flies aren't attracted to light so much as confused by a navigational accident. To fly north, a flies keeps the rising moon of its right shoulder. Trying to keep a porch light continually off your right shoulder results in pandemonium.

Other sources disagree with the moon hypothesis and note that flies actually veer away from the light source at the last minute. To the flies, the area just outside of the light appears darker. Flies, being nocturnal, head towards the dark patch, which is always just around the light, hence the confusion.

Finally, the BBC, in a very genial British way, notes that the issue remains unresolved and presents both hypotheses. We're with the BBC.

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