Butterflies and moths make up the Lepidoptera. The name means "scale wing," and lepidopteran wings are covered with microscopic scales, which are iridescent and brightly colored in the case of this California butterfly, Lycaena helloides. The scales are visible as the "fuzz" along the edges of the wing. Primitive lepidopterans retain functional chewing mouthparts as adults, but more derived ones have partially or completely lost the mandibles and developed a long proboscis for drinking nectar from flowers.
The first definite lepidopteran fossils appear in the Lower Cretaceous, though lepidopterans are not common as fossils. Their evolution has been closely tied with the evolution of flowering plants, which also appeared and began to diversify in the Cretaceous. Among the butterflies, both adult and caterpillar stages feed on flowering plants, and the adults are important pollinators of several flowering plant families.
For more information:
The Butterfly WebSite contains information and links for butterfly aficionados of all sorts and conditions. Another extensive list of electronic resources on Lepidoptera is maintained at Dalhousie University in Nova Scotia, Canada. Many more images of lepidopterans are available from Phillip Greenspun's excellent archive, or from the Smithsonian Photo Server at the Smithsonian Institution, National Museum of Natural History.
The Marine Biological Laboratory at Woods Hole, Massachusetts, has made available Rudolph Leuckart's 19th century zoological wall charts; click here for his chart of lepidopteran anatomy. For more on lepidopteran life histories, you can get pictures of the gypsy moth at various stages in its life cycle from the Gypsy Moth Home Page at Virginia Tech.
Aficionados of the most famous North American lepidopteran, a certain Danaus plexippus, should definitely check out Monarch Watch at the University of Kansas Department of Entomology.