To keep themselves warm during cold weather, butterflies spread their wings in the sun. The wings of some species of swallowtail are remarkably efficient at trapping and absorbing sunlight. The insects’ secret lies not just in their dark pigment but also in the structure of microscopic, overlapping scales coating their wings.
The scales, in turn, contain rows of honeycomblike holes separated by inverse V-shaped ridges that funnel light into the holes. This ingenious structure traps incoming sunlight, making the wings extremely black and warming the butterfly with amazing efficiency.