Butterflies and moths belong to the order Lepidoptera. This name means "scale-wing" in Latin and refers to the scale cell structures found on the wings. As is usually the case with insects, the closer you study them, the more you`ll discover. Butterfly and moth wings are marvelously elaborate structures above and beyond the beauty of their patternation. The wings are predominantly a transparent or brownish epidermal membrane no more than 2 cell thick that spans the spaces between a network of wing veins that fan out into the wing shape. The shape and size of wings varies between species and usually takes on a characteristic shape that may include scalloping, lobes and even trailing hair-like slivers.
The scales grow out of the epidermal membrane and are comprised of a basal socket cell and a flattened scale cell. In the case of butterflies, these scales are organized into orderly rows that radiate out in a perpendicular fashion to the base of wing. In comparison, most moths have a random distribution of scale cells. There are generally two types of scale cells. Ground scales are typically small and carry the background coloration of the design. A second type is known as the cover scales and are usually larger and more colorful, bearing the main pattern elements of the particular design
If we take a closer look at the individual scale cells, we notice they vary considerably in size, shape and structure. Scale cells are generally held at a 45 degree angle to the wing membrane. The exposed top surface of these scale cells have an elaborate extra cellular structural architecture known as fenestration. These micro structures play an important roll in the iridescent color characteristics of various butterflies. The tiny structures interfere with light wavelengths and usually result in brilliant shimmering blues and greens. The multitude of other colors found on the scales of butterflies and moths comes from pigmentation. Each scale cell holds a single color pigment that include melanins, ommochromes, pterins, and flavonoids derived from plants.
Observing patterns as a whole, we notice that the left and right wing designs are generally symmetrically along the axis of the body. The dorsal (top) forewing, dorsal hindwing, ventral (underside) forewing and ventral hindwing represent the four wing surfaces that carry a unique pattern on each butterfly species. The dorsal wing surfaces typically display bold, simple and colorful designs, whereas the ventral surfaces are notably more detailed. This phenomenon corresponds with the fact that the dorsal surfaces are generally visible during the rapid undulating wing beats of flight compared to the detailed and often cryptic ventral surfaces which are encountered in plain view as the stationary butterfly assumes a resting position
Another interesting observation about wing patterns is referred to as Oudemans` principle. As you study the ventral wing pattern of a resting butterfly, you`ll notice the pattern often smoothly translates from the hindwing to the visible tip portion of the forewing. In contrast, the covered portion of the forewing lacks the patternation and is often more brightly colored making for a disorienting flash of color as the butterfly launches into flight. Oudemans` principle can also be observed on the forewing patterns where design element align between the fore and hind wings when the butterfly is displaying its dorsal surfaces.
A fair volume of research has been conducted into the analysis of pattern element along with exploration into the developmental mechanisms of pattern formation. A good portion of this article was inspired by H. Frederik Nijhout`s book, "The Development and Evolution of Butterfly Wing Patterns." Studying the commonality between the bewildering diversity of patternation found on the wings of butterflies and moths resulted in a generalize model of pattern elements and symmetries known as the Nymphalid ground plan. Although no single butterfly species exactly manifests all the pattern elements established in this model, it forms a useful reference framework to discuss the specific elements of any particular design. This model was initiated back in the 1920`s by B.N. Schwanwitsch and F. SЁ?ffert. The model identifies regional bands of symmetry that radiate out into the wing plane from the root where the wing attaches to the thorax. Reviewing the pattern elements of the model from the root out to the wing tips we find a wing root band, a basal symmetry system, a central symmetry system, a discal spot, border ocelli complex, parafocal elements and marginal bands. The model is enhanced with the recognition of venous strips as a major pattern element