Tea and Toast

"It's about prevention, not cure, she said." http://www.bbc.co.uk/news/world-11949956 #wikileaks

I took this photo of a moth in a cave over the weekend, and ever since it has been puzzling me: photo

I can just about get to grips with the idea that the better camouflaged moths are more likely to survive longer than the less well camouflaged ones, thus allowing them a greater chance of mating with another: the result being moths which are better camouflaged to their environment over time. And I assume this is the mechanism at work here.

What has been occupying my mind is the fact that the camouflage is symmetrical. Why?

Is it simply the 'average camouflage'? Or is it that, like elevator music, it can't please every background (which inevitably are all naturally chaotic in appearance) so it eventually finds a pattern which will suit no background perfectly and not favour any particular pattern, which would look very obvious against another very different background pattern?

In summary, is it symmetrical because no background it ever encounters is?

Elevator music is designed not only to please no one, but to irritate everyone, so perhaps it isn't the perfect analogy, as I'm sure you'll agree this moth is admirably disguised.