Like a moth to a flame
Moths are drawn to flames, to bright lights, and as any good moth-er knows, ultraviolet. But why? That question has no answer although there is plenty of #DeceivedWisdom.
The first and perhaps most well-known explanation as to why moths are drawn to light is that they normally use the moon to navigate and an artificial light confuses their bio-satnav. This is very unlikely. Most moths don’t migrate and in general, don’t need to navigate. But, some moth-ers might say, there is always less of a haul in the UV scientific trap on nights when there is a full moon. The obvious answer to that is that moths are simply less active because the night is brighter and the majority that is drawn to light will not be drawn when the night’s too bright because of the moon.
Lots of species aren’t drawn to light at all, they prefer odour and specifically the pheromone odour of the female, at least that’s the case of the day-flying males of the Small Emperor species, discussed here previously. There was a theory in the 1970s that suggested male moths somehow confuse the light source with the luminescence of the female’s sex pheromones. But, while those pheromones can be made to glow under certain conditions, generally in a laboratory, they don’t glow at the same wavelengths as ultraviolet. More to the point, females are drawn to light too, so it’s not about moth sexual attraction.
There are actually no good theories to explain why some, but not all moths, both male and female, are attracted to light and not even all wavelengths of light but commonly ultraviolet-A and white light, but commonly not yellow, despite, that “moth to a flame” aphorism.
I wonder whether there’s some kind of confusion happening, but cannot explain why it only happens for certain species, there are 160 000 species of moths in a wide range of taxonomic families, and some species across all families are not drawn to light. Might their confusion be some kind of synaesthesia – where there is a kind of “crosstalk” between senses (the same kind that means some people can smell colours or have a visual experience when they hear music). Could those moths that are drawn to light be anticipating something else, maybe the light “smells” like food (or the aforementioned sex attractants but in some kind of synaesthetic way. The former wouldn’t explain why some moths that have no mouthparts and don’t eat are still drawn to light.
So maybe it’s more of an all-encompassing effect…could it be that the bright light or the ultraviolet saturates their senses and stimulates the reward neurones in their brains as might orgasm in higher animals or, indeed, opium derivatives, and doing so in such an intense way that they cannot help but be drawn to that flame.
I asked a couple of experts what they thought:
Juhan Javoiš of the University of Tartu in Estonia suggested that the navigation idea may well be the most plausible: the moths look at the moon just to keep going straight. Navigation is probably necessary not only for migration, but to keep direction, in order to move on more effectively (towards the partner, or oviposition substrate in some females maybe) (olfactory cues are not as stable in air as is light. So, maybe something like this: sniff – fly – sniff again – fly again). indeed, females come much less often to light than males, he told me. But, adds that oother explanations, including mine, cannot be excluded.