Butterfly Flight: Wing Structure, Color and Function

The fluttering flight patterns of butterflies have long inspired poets but baffled scientists. Researchers have struggled to understand how these delicate creatures can fly with their large but inefficient wings.

  The Basics

Butterfly wings come in a variety of colors and patterns.

A butterfly has four wings, two forewings and two hindwings. They are attached to the second and third thoracic segments (the meso-thorax and meta-thorax). Strong muscles in the thorax move the wings up and down in a figure-eight pattern during flight.

When the fully-grown adult butterfly emerges from its pupa (chrysalis), its delicate wings are crinkled, wet, and uninflated. The butterfly hangs upside-down and pumps blood into the wings to inflate them. It must then wait for the wings to dry before it can fly.

When the fragile wings fray or are torn, they do not repair themselves.

  Wing Structure and Scales

Butterfly wings are made of two chiton layers (membranes) that are nourished and supported by tubular veins. The veins also function in oxygen exchange (breathing). Covering the wings are thousands of colorful scales, together with many setae (hairs).

The name Lepidoptera (which includes butterflies and moths), means "scale wing" in Greek. These wing scales are tiny overlapping pieces of chitin on a butterfly or moth wing. The scales are outgrowths of the body wall and are modified, plate-like setae. The front and back of the wings usually have different patterns.

Scent scales are modified wing scales on the forewing of male butterflies and moths (on the costal fold) that release pheromones. These chemicals attract females of the same species. Scent scales are also called androconia.

  Wing Color

Many butterflies are brilliantly colored, while others are drab. There are often ultraviolet patterns in the wings that we cannot see, but which may be seen by other butterflies. Even many of the colorful species have drab-colored outer wings (that are visible when the animal is at rest). The coloration of these insects serves many purposes

  Camouflage, in which the color of the animal helps it blend into the environment, hiding the insect. The Australian leafwing butterfly, for example, is shaped and colored like a leaf.
  Warning (or aposematic) coloration: brightly-colored butterflies and moths are either bad-tasting or a mimic of similar-looking bad-tasting butterflies.
  Attracting and finding mates, who look for certain colors and patterns.
  Deceiving predators into thinking they're bigger than they really are. Some wings have large "eyespots" which make the butterfly or moth look like the face of a larger animal (like an owl), scaring away some predators.
  Soaking up heat: dark-colored scales soak up heat very well when the butterfly suns itself. Like all insects, butterflies are cold-blooded. When they get too cold, they warm themselves in the sun.

Butterflies actually get their colors from two different sources: ordinary color (or pigmented) and structural color.

  Ordinary Color

Butterfly Wing Structure
Basic Butterfly Wing Structure Showing Veins

The ordinary color comes from normal chemical pigments that absorb certain wavelengths of light and reflect others.

For example, the pigment chlorophyll colors plants green. The chlorophyll soaks up the blue and red colors of the spectrum, but not the green, which you see when it bounces back to your eye. Most butterflies get their different shades of brown and yellow from melanin, the same pigment that makes you tan in summer and gives some people freckles.

  Structural Color

The structural color of butterflies is where things get interesting. This type of color stems from the specific structure of the butterflies' wings and explains why some of a butterfly's colors seem to shift and appear so intense. This quality of changing colors as you, the observer, moves is known as iridescence. It happens when light passes through a transparent, multilayered surface and is reflected more than once. The multiple reflections compound one another and intensify colors.

  Wings In Flight and At Rest

  Coupling of the Wings

Butterfly Mating

During flight, the forewing and hindwing are held together and function as one wing. The coupling mechanism differs in different species. In most butterflies, a lobe on the hindwing presses against the forewing. In most moths, bristles on the front edge of the hind wings (called the frenulum) connect with hooks on the hind edge of the forewing.

  Wings At Rest

When at rest, butterflies hold their wings vertically. Moths hold their wings horizontally when at rest. A monarch butterfly at rest is pictured to the right.

Further Information:

 Butterflies and Moths of North America
 Southern Wisconsin Butterfly Assn (NABA)
 The Butterfly Site

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