Why Are Moths Attracted to Light?

Q: Why are moths attracted to light?
Insects, Clayton North Carolina

A: The current theory is: moths are not attracted to light. They fly towards an artificial light as a navigational accident.

Over the millennia, moths navigated at night by the light of the moon. To fly in a given direction, they would keep the moon in a fixed location, relative to their bodies. For example, to fly north, they would keep the rising moon over their right shoulder. However, a porch light, for example, is brighter than the moon for a moth flying nearby so he confuses my porch light with the moon--thinking the brighter light is the moon. Unfortunately, keeping my porch light over his right shoulder only works as he flies directly by. As he gets a little bit past, the light is behind him. So he turns to get the light opposite his shoulder again. And ends up spiraling into the light with every correction he makes. That's the theory.

But, as anyone who watches moths around porch lights knows, not all moths spiral in. Many, many moths fly directly at the light source with little indication of any spiral, says Dr. James K. Adams, professor of natural sciences at Dalton State College.

We don't have another generally-accepted theory which explains both why some moths spiral and others don't.

By the way, some night-flying moths, says Adams, migrate using the moon as a primary reference and calibrate that reference with their internal geomagnetic compass. Every hour they alter their flight path by 16 degrees to correct for the travel of the moon across the sky (the Earth's rotation). On moonless nights they navigate solely with the geomagnetic compass.

Further Reading:

Dalton State College: James K. Adams, "Why are moths attracted to lights"