Bombyx mori 300 to about 900 m (1,000 to 3,000 ft) long. The fibers are very fine and lustrous, about 10 μm (0.0004 in) in diameter. About 2,000 to 3,000 cocoons are required to make a pound of silk (0.4 kg). At least 70 million pounds of raw silk are produced each year, requiring nearly 10 billion cocoons. Due to its small size and ease of culture, the silkworm has become a model organism in the study of lepidopteran and arthropod biology. Fundamental findings on pheromones, hormones, brain structures, and physiology have been made with the silkworm. One example of this was
Bombyx mandarina differ in karyotype from those of inland China. Domestic silkmoths are closer to the latter regarding mtDNA sequence data, and especially lack some genetic apomorphies of the northeastern "B. mandarina". Thus, the initial domestic stock came from inland China. "B. mandarina" is able to hybridize with "B. mori". Both in the wild and in a domesticated environment, females release pheromones and wait for males to be attracted and fly to them. However, "B. mori" males cannot fly. Hybridisation in the wild, therefore, inevitably means breeding between domestic ("B. mori") females and wild ("B. mandarina") males. Hybridization is possible in both