Why Are Moths Drawn to Light?
You’ve probably heard the expression “like moths to a flame” used when someone is hopelessly attracted to something that’s killing them. If not, maybe you’ve seen the now-dated moth meme, or you’ve been out camping, or you’ve been on your porch. The long-short; you likely have, at some point, seen moths attracted to light. There’s truth in the idiom too; this is self-destructive behavior for the moth. So why are moths drawn to light?
The answer is a bit more complicated than you might think, and there’s no clear answer. But there are some things we’re pretty sure about, so we’ll get into it while also discussing the complications of them.
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Moths Use Light as a “Compass”
We know that moths fly and direct themselves using a process known as transverse orientation. They kind of fixate on a light source, and make sure they fly at a consistent angle to it. Moths evolved this way before humans started putting porch lights up, and they’ve been flying around since there was just the moon.
So imagine a moth using a lamp as its “moon” for orientation. Once it invariably ends up too close or above the lamp, the moth will try to course correct to maintain the angle it once had. This leads to the moth basically spiraling towards the light. A moth may further confuse itself once there are multiple light sources, as is likely in the light-polluted environments most of us live in.
There’s a problem with this, though. We have proven that moths can evolve to avoid artificial light. Plus, even though we haven’t had light bulbs for very long, we most definitely have been making fire for a really long time.
If messing with the moths’ ability to self-orient is the only thing getting to them, then evolution would have weeded out all the moths that flew into fires long ago, right? There’s also the added wrinkle of migration–not all moths do so. If you’re not a migratory moth, why would you need to dedicate so much to light-based orientation?
Light as an Escape Tool
If you’ve disturbed a bunch of still moths before, you may have seen them fly upwards–likely towards the moon. It’s possible that, in line with transverse orientation, that moths instinctively fly towards lights when they’re in danger. Your big scary human body might be scaring them so they fly where they think is up (the moon). Which ends up being your porch.
Moths Might Want to Mate With Fire
We’re not saying your pet moth is sexually attracted to fire, we promise. We’ll explain.
Some infrared light emits at a frequency identical to, you guessed it, candlelight. Which means that when moths see some types of fire (remember moths are evolved to look at very dim light) they think a female moth might be emitting the mating pheromones. Sadly, the moth attempting to mate with the candle will not create a supermoth that breathes fire. It just dies.
However, moths are still attracted to UV lamps and other frequencies, so this likely isn’t the full explanation either.
Moths Think Artificial Light Is the Sun
Moths aren’t very smart (give them a break–some of them don’t have mouths). So while they might think your lamp is the moon for orienting, when they get really close to it and realize it’s super bright, they might change their tune.
This might explain why moths just kind of sit and stare at lights for a long time. Moths are nocturnal, and they’re only active when it’s dark. We’ve even seen that moths are less active during a full moon, likely because there’s more light from a full moon, so some moths will think it’s still day. This also means, then, that moths don’t have an internal clock, but we digress.
There’s still a lot we don’t know about why moths like light so much, and we can only throw theories around and see what works. Regardless, our artificial lights don’t look like they’re going to stop killing moths soon. Hopefully these not-so-bright bugs can figure something out.
Show some love to our light-loving friends here.