The real question is: why is this in the adult section? Seriously, there's actually a category called "butterflies".

Aside from their traveling methods and therefore explaining the wing shape, butterflies are ''pretty'' due to three main reasons. One, a defense mechanism. Flashy and all, the colours can confuse or even scare other predators, especially while in flight, and some butterflies have shapes or patterns on their wings which may instill fear in predators. It could look like faces, although I never quite understood that, especially not the Death Head Moth...how does an animal or insect ''know'' what death is, and how can it therefore be afraid of a skull shaped pattern? Well, most likely it isn't that at all, but instead looks more like another animal or something that the would be predator sees as a threat. Also, many butterflies are venomous, and some predators recognize the colours as such on some butterflies somehow, and ''know'' not to eat it, else they will be sick or even die. The Monarch, for example, is extremely poisonous if a bird or other insect should eat it. The warning is somehow ''portrayed'' in the flashy wings, because other then rendering the predator ill through consumption, the Monarch has no means of dispensing and distributing any poison whatsoever. It's not really poison either, just a really hazardous biological construction. Butterflies have no real means of defense at all, so the colours on the wings and their effect on some predators is extremely amplified, unlike most other insects which have more efficient means of defense or escape from predators. The second reason is for mating purposes. Take two butterflies of the same kind, of both genders, male and female. The male always has bigger wings, and the colours are always brighter and flashier, in most cases. This is how a male butterfly attracts females for mating, sometimes through flight shows or just ''being'' there. Incidentally, compare the female again, her wings are smaller and darker, and her body is fatter and not as long as the male, this is because she needs to be bigger in order to contain the eggs. And third, butterflies use the warmth of the Sun for ''motion energy'' in order to be able to fly. (Nocturnal butterflies are the exception, they rely on pure strength, notice the two different methods of flight in both day and night butterflies.) The ''colours'' on the wings of butterflies are actually all these thousands of little scales attached to the wing, and the colours shine and reflect sunlight as a result of ''being imbued'', therefore makes them look all funky. Notice a butterfly which is at rest and is slowly closing and opening its wings; this is the ''Sun Feeding'' method. You'll NEVER see butterflies out on cloudy days, and if you do, you can probably catch it easily without it being able to get away. What I've listed stands for just about every butterfly which lives during the day, although I'm pretty sure there are many exceptions.

they don't have backbones.