Butterflies give bugs a good name.

Indeed, they are the supermodels of the insect kingdom, garbed in spectacular colors and sensational designs.

However, all that artistry has more purpose than merely to please the human eye. The hues and patterns carried on those fragile wings in fact have multiple purposes, all of them critical to survival - discouraging predators, generating heat and wooing the opposite sex.
The design of butterflies is quite ancient. And judging by how little it's changed over the years, it's been very successful. Nature doesn't fix what isn't broken.

Human beings have only been around about 2 million years, but physically and intellectually we are a species that has changed dramatically. Butterflies, on the other hand, have been flitting from flower to flower and sporting colorful patterns on their wings for more than 40 million years, with few evolutionary alterations.

'The features we identify with butterflies haven't changed very much - the body shape, the larger details of the wing patterns, the way the wings are shaped and organized,' said Adam H. Porter, an evolutionary biologist at University of Massachusetts in Amherst.

Butterflies did not deliberately aim to have the specific colors and patterns they have. The process began more or less by accident, the result of genetic luck, the way human brothers with the same parents might be of different heights, weights or hair color.

In this way, over millions of years, luck and genetics may lead to a species of butterfly that is extremely well camouflaged around maple trees. This is called natural selection.

Other features of butterflies evolve in the same manner, taking hold in a species because of the advantage they give it in surviving.

For instance, some butterflies have evolved to have a feature on their wings called eyespots, which help to discourage predators. The little wood satyr has a pair of eyespots on the edges of both its front and back wings. They are spots that may appear to a poor-sighted predator to look like eyes, Porter said.

'They can startle a predator like a bird or snake, buying the butterfly an instant of time in which to make its escape,' he said.

Natural selection also put the 'tail' on the swallowtail. Swallowtail butterflies have small projections at their ends of their wings that look like tails. They evolved to attract the attention of predators who may attack the false tails, which tear off easily.

'There's been recent research showing that the wings in this area are especially fragile, like a tearaway football jersey. A naive bird, which hasn't had a lot of experience with butterflies, might bite at the thing, tearing it off, but the butterfly will be able to escape.

'Often, you find butterflies missing this portion of their wings, and that's sometimes the reason,' Porter said.

Fred C. Gagnon, an entomologist and the curator at the Magic Wings Butterfly Conservatory and Gardens in South Deerfield, said some butterflies have evolved to be poisonous, making birds and other predators sick when they eat them. Interestingly, other butterflies have evolved through natural selection to have similar colors and markings as the poisonous butterflies, called mimicry.
'They mimic poisonous butterflies to avoid being eaten. For instance, the viceroy butterfly mimics the monarch (which is particularly distasteful to predators). If a bird eats one and discovers it's poisonous, it will not want to eat the other. So the butterflies that look the most like what a predator will be afraid of will be more likely to live and will be more likely to pass those genes along to offspring,' Gagnon said.

Butterflies, like snakes, frogs and turtles, don't have a way to create heat inside their body, the way humans do. They are the temperature of their surroundings and often have to warm up by basking in the sun.

Dark colors, such as brown and black, absorb more sunlight than light colors, such as yellow or white, and the absorbed sunlight creates heat. For butterflies, which need a way to generate heat on a cool day, this phenomenon is important.

That's because butterflies need a body temperature of at least 80 degrees to fly well. Their muscles won't work properly otherwise. For this reason, butterflies that fly in the early spring or late fall or that overwinter as adults in New England, such as mourning cloaks, tend to be dark colored.

'However, the need for dark colors farther out on the wings isn't as great as it is near the body. That's because very little blood circulates in the wings and they are only able to transfer heat for a short distance,' Porter said.

Reproduction does require bright colors and distinctive patterns somewhere on a butterfly - not only to attract the eye of the opposite sex, but also to identify it as being of the same species.

'Females are making decisions based on how nicely and brightly colored the males are. Males are doing the same,' he said.

Once you know all this, an eastern tiger swallowtail's coloring makes a lot more sense: dark near its body for heat, false tails on its wings to foil predators, and fantastic yellow coloring with black patterns on most of its wings to lure a mate.