A lustrous play of colour alchemy, iridescence can intrigue, camouflage and incite desire. Laura Parker immerses herself in one of Nature’s greatest special effects
IT took 1,000 beetles to make one of the most celebrated dresses of the 1880s. Audiences gasped when Ellen Terry made her entrance as Lady Macbeth, her costume shimmering with the sheeny wings of green jewel beetles. The showstopper caused Oscar Wilde to remark that Shakespeare’s villainess evidently ‘took care to do her shopping in Byzantium’. Society portraitist John Singer Sargent, who loved to paint lustrous fabrics, was also captivated and the actress posed for him, arms uplifted, crown held aloft, in what was to become one of his most arresting works.
The theatrical trick that dazzled them all was iridescence. One of Nature’s special effects, it occurs when a surface appears to change colour, depending on the angle from which it is viewed. Jewel beetles are some of its glossiest exponents, the many reflective layers of their wing casings producing metallic greens and blues. These have been used decoratively in Asia for centuries, embroidered into clothing and appliquéd to leather. The ancient Egyptians placed them reverently in burial chambers: crushed to a powder, they decorate a cane in Tutankhamun’s tomb. W. B. Yeats was right to say ‘eternity is in the glitter on the beetle’s wing’.
Iridescence is found throughout Nature—in birds, molluscs, fish and even plants, as well as insects. It has a vast palette, from the delicate pinks and teals of a soap bubble to the showy turquoise and bronzes of a peacock’s ‘eyes of God’. It appears to have a range of functions, some rather prosaic when compared with how it is prized. An oyster shell’s silky nacre, or mother-of-pearl, is a protection from parasites and irritants, built up of composite layers of calcium carbonate and protein. In birds, iridescence is a signal to attract potential mates or to ward off enemies and claim territory. For something so flashy, it is a surprisingly useful disguise. Even the most lurid beetle can remain camouflaged amid shiny leaves in dappled shade. The celadon-coloured underside of the green hairstreak butterfly’s wings blends beautifully with the blaeberries in its heathland habitat. Iridescence also provides further protection by making predators think twice about attacking. Its role as a means of communication among airborne creatures is still being explored.
We have always be
