Why are flies attracted to lights?

The short answer is scentifically we dont know. However there are theories out there that try to explain this. One theory is that flies 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. To fly north, flies keep the rising moon on the right shoulder. Trying to keep a porch light continually off your right shoulder results in pandemonium.