Cocoon stage is important in a life cycle of silk because it gives thin thread of silk when boiling and thread of single silk fibre is too fine so upto ten cocoons are wound together onto a reel by hand . each cocoon is made from a single silk fibre around 1km long.
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The fibres are triangular prism like structure. so the silk cloth refracts the light falling on it at different angles and gives a shimmering appearance.The cocoon of the silkworm is produced by the animal in a trianglular shape, so that for the length of the strand, light is reflected from most any angle.