Elongate cavities and skin-core structure in Nephila spider silk observed by electron microscopy

Major ampullate silk fibres from the orb-weaving spider Nephila madagascariensis were analysed by transmission electron microscopy. The fibres have a thin outer layer surrounding a column of apparently homogeneous material which contains elongate cavities orientated parallel to the silk fibre axis. The cavities appear similar to 'elongate vacuolar droplets' observed in the silk of Antheraea silkmoth larvae. The overall skin-core structure is probably the result of a rheological pattern originating in the two secreting regions recognized in Nephila silk glands; the cavities indicate material inhomogeneities.