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
Dauer larva as "L1", "L2", "L3" and "L4". After L4, animals moult to the reproductive adult stage. However, when the environment is unfavorable, L1 and L2 animals have the option to divert their development from reproduction to dauer formation. Signals such as temperature, food supply, and levels of a dauer-inducing pheromone, a population density cue, influence this dauer decision. Dauer larvae are thus considered an alternative L3 stage larva, and this stage is sometimes preceded by L2d. L2d animals are considered pre-dauer and are characterised by delayed development and dark intestines produced by storage of fat. L2d larvae can either continue normal