Moths and light

Sydney has been apparently hit pretty hard by the bogong moth migration this year. Not that I could care about Sydney - even though I've just recently been there it's not in my backyard. It's more than six hours drive, placing it well outside of my care zone. Just lately though, it seems there's a hell of a lot more moths everywhere. My cat has been having a ball. You hear a thunk! and it's her head smacked up against the kitchen window with a freshly caught moth in it. Or you see a leaping form as she catches one mid-air.

I was chatting on MSN last night and in dire want of a cigarette, so I just up and took the laptop outside with me. Under the outside light. It was a less than brilliant move that led me to be buzzed far too many times and gather a nice group of them on my screen. They do not seem to be deterred by smoke.

So it brings up that eternal question - why? Why are these little tykes attracted to the light anyway?

In a quest to find out a little more I discover the concept of phototaxis. This occurs when a whole organism moves in response to light. So the moth is an organism that is positively phototactic. It moves toward the light source. On a nice day, I also become positively phototactic. With a hangover, however, I become negatively phototactic and attempt to remove myself from the source of light.

Some theories say that the moth uses the moon as it's navigational source during migration. So when they encounter a much closer light source it results in confusion. I can just imagine it - Holy shit guys it's the moon!!!! I made it!!!...
... now what do I do?

Or maybe it's just one big disco party for them all.

Another idea is that moths, being night-flying creatures, go into sleep mode as they encounter a source of light. It's an artificial daytime for them, therefore time to sleep. Kind of like the egg-producer's practice of keeping the lights on so the chickens still think it's day, therefore time to lay.

But there's another, alternative theory. This one I like the best especially because of the research behind it. Henry Hsiao showed that moths can be drawn toward a light source from up to 200 feet away, but when they get close, they circle it. This is because the bright point of light affects the eye of the moth in such a way that it causes them to perceive a very dark band around the light source, a Mach band. In fact, all seeing creatures have this. The moth tries to fly into the dark spot to avoid the light. Eventually momentum carries it away. So maybe the moths that end up sitting on my laptop screen are just buggered from this circling idea and need a rest.

The best thing about that theory is the research. This guy is like one of those kids in primary school who pulls the wings off flies to see if they can go in circles (actually... I was one of those, too). Except this guy Hsiao gets paid for it. It's now research. He tethered moths to little styrofoam boats in a tiny artificial pond and tracked their flight as they headed toward a light source. I can just imagine it - a moth with a pin in it's arse tied to a bit of string, dragging a styrofoam boat across a pond. Ten points for ingenuity.

I want to give it a go myself.