What is the powdery material that sticks to the fingers when a butterfly is caught by its wings?
GEORGE VARGHESE
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Both butterflies and moths belong to the order Lepidoptera meaning scaly wings. As the order name Lepidoptera implies, the powdery material found on butterfly wings that sticks to our fingers is a bunch of tiny scales, modified sensory structures called setae. Wings are made of two thin membranes covered with unicellular scales arranged loosely in rows. Thin layers of chitin, a hardened protein make the scales. These scales strengthen and stabilize the wings. The scales are of two kinds, one filled with colouring materials and the other minutely grooved and surfaced.
Each scale is plugged into a socket on the wing with grids of high and low ribs and cells. The cells hold the natural pigment molecules such as uric acid (white), carotenoid pigments (yellow, orange), quercetin (red, purple) and melanin (brown). Each pigmented scale produces only one type of pigment. Along with the pigments, the arrangement and spacing of the ribs and cells also contribute to the colour. However, the vivid iridescent colours are the results of reflection and refraction of light by the different size, pattern and spacing of the ribs on the scales.
Besides regulating temperature by either absorbing or reflecting sunlight, the loose attachments and slippery nature of scales prevent butterflies from predators. Some species have androconial scales helping in the dispersal of pheromones to attract the opposite sex.
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AZHWAR RAGHUNATH
Research Fellow
Department of Biotechnology
Bharathiar University, Coimbatore, Tamil Nadu
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