Authored by Kennedy Allen in Nature and Wildlife 
Published on 10-09-2009

It is common knowledge that some insects are attracted to light. While the exact reason for their seemingly endless fluttering around the street lights is still under debate, there are some things scientists have figured about why some insects are attracted to light and why others are repelled by it.

Moths are a common example of the usual suspects found fluttering around lights left turned on at night. The opposite of these moths that are attracted to light are cockroaches, which run and hide as soon as a light is turned on in their vicinity. This is explained by a natural phenomenon called phototaxis which can be positive or negative depending on the bug and their reaction to a light source.

Insects that are attracted to light have positive phototaxis. Moths, flies, and other varieties of night flying insects fall under this category. There are a few hypotheses as to why these insects are attracted to lights. The first hypothesis relates to the insects’ suspected internal navigation. Moths are said to migrate north. For this to happen, a moth must keep the rising moon on their right side. If the moth is confused by an alternate light source (i.e. the garden lights) they are bound to wind around and around the misidentified moon while attempting to keep it on their right side.

The next theory indicates that insects are attracted to light for their own protection. It is believed that maybe these light bulb circlers might not have the proper components in their eyes to adjust from light to dark, so once they are exposed to the bright light it is difficult to fly away. Being as to how their eyes now have a difficult time seeing in what is deemed a darker area away from the light source, the insect automatically stays close to the light where it can see potential predators. Instead of flying away into an area where they cannot see well anymore insects flutter around the lights for safety.

These hypotheses have never been proven right or wrong because there are arguments against both. On the theory that constant circling of lights is caused by migratory confusion, there have been experiments done that have the bugs attracted to lights and then introduced a natural light source, yet the insects still kept fluttering around the bulbs.

Then, about the theory on the bugs staying close to the light source to avoid being consumed by predators is the evidence of lizards, frogs, and bigger beetles camping out around light sources waiting for the easy meal. Not exactly the safest place for a fly if they can so clearly see what is coming for them.

Now, on the other side of the phototaxis scale are the insects like cockroaches. Insects that are repelled by light are considered to have negative phototaxis. This is why when entering a room and turning on a light one may catch some quick scurries from insects trying to hide away. Personally, watching the insects fly around the porch light sounds much more appealing.