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
Maru Maru Mori Mori! the record of the longest streak on the Oricon charts. The previous record set by the 2007 song "Gake no Ue no Ponyo", the theme song of the Studio Ghibli film "Ponyo", which remained on the charts for 11 consecutive weeks in 2008. "Gake no Ue no Ponyo" featured the then 8-year old actress Nozomi Ōhashi. The song "Maru Maru Mori Mori" received the Special Award at the 53rd Japan Record Awards. Maru Maru Mori Mori! On 4 April 2011, it was announced that the theme song of the Fuji Television television drama "Marumo no Okite" will be sung by