Tag Archives: Philip Callahan

Like a Moth to a Flame

I was asked by a friend, “So, why are moths attracted to lights? Do they think they are flying to the moon?” The quick answer is, “No”. Why would a moth, or indeed any insect, want to fly to the moon?

That kind of behavior is unwise and bodes ill for the long term existence of your species, especially if your species shows a remarkable lack of certain intellectual skills, skills like the forming of, and testing of, hypotheses. And then converting those hypotheses which have been proven correct, and are therefore proven theories, into actual tools, tools that let you build more tools, and, ultimately, fly to the moon without freezing or suffocating on the way.

No known species of moth has done that, in the same way that no known scientist has actually figured out why moths fly into lights. That’s not to say they haven’t tried. There are a number of hypotheses, but no proven theories.

Some think that, since moths evolved with no artificial light sources around, their navigation systems are screwed up by human light sources. But moths have had lightning bugs, glow worms, wildfires, and volcanoes around and they deal just fine with those, and our yard lights are not that much different.

There is one hypothesis, though, that I am partial to, even though it has some flaws, too, but it does a better job of covering the problem than the others.

The hypothesis is by Philip Callahan. Who, working in the 1970’s as an entomologist with the U.S.D.A., suggested that an insect’s antennae should be looked at as antennae. Antennae as in a radio antenna, and not some sort of buggy equivalent of a nose.

The usual view is that, in moths for example, the male cruises through the air using its rather fluffy antennae to sniff out the pheromone scent trail his mothy lady love has laid out in the breezes before him. The chemical snags on the antennae, which were presumed to have little sockets that fit the shape of the molecule, which in turn sets off the neural signal telling Romeo he is on the track of Juliet.

Callahan, who is much more than an entomologist, looked at the male moth antenna, and wondered what frequency of electromagnetic radiation it could be tuned to. He did the calculations and determined that they should pick up a spectrum of infrared wavelengths.

He got some of the female moth pheromones, put them in a bottle, put a bright light on them, and the male moth wanted to fly at the bottle. Turn it off, and he lost interest. It turns out that the pheromone absorbs light at higher frequencies, especially ultraviolet, and re-emits it as infrared. The male moth is following a trail of light, wafting in the gloaming light of dusk. It could be that many insects do the same.

So, it could well be that the one of the reasons bugs are attracted to lights is that, since all our lights give off some heat, which is infrared radiation, we are telling them to come get some sweet, sweet, lovin’. And then they die.

First shared on the Squatcher’s Lounge Podcast:

For the reading impaired, an audio version of this quasi theory may be found here: