Disclosed are transgenic silkworms engineered to posses and express a chimeric spider silk protein gene, the chimeric spider silk protein gene encoding a chimeric spider silk protein having spider silk domains specific for a spider silk elasticity motif sequence and/or a spider silk strength motif sequence. Also provided are improved silkworm silk fibers having improved strength (tensile) and elasticity characteristics relative to native silkworm silk fibers. An improved method for preparing chimeric silk fibers employing the transgenic silkworms disclosed herein is also provided, the method employing a piggyBac based vector system and a helper plasmid. Genetic expression cassettes are provided, and are used to create a number of synthetic spider silk encoding sequences (Spider 2, Spider 4, Spider 6, Spider 8). A piggyBac vector system is used to transform mutant silkworm, in the presence of a helper plasmid, to incorporate the chimeric spider silk gene into the silkworm to provide a stable transformant. These transgenic silkworms thus provide an efficient spider silk producing organism suitable for commercial production of silk fibers.
