how do these species release that material?
By forming a cacoon by this insect
Bombyx mori
he cocoon is made of a thread of raw silk from 300 to about 900 m (1,000 to 3,000 ft) long. The fibers are very fine and luscious, about 10 μm (0.0004 in) in diameter. 
when did silk begin to be produced in china th millennium BC can you name some species from where we obtain this material? Bombyx mori
wiki:13484574
Bombyx mori [SEP] Cocoon
The cocoon is made of a thread of raw silk from 300 to about 900 m (1,000 to 3,000 ft) long. The fibers are very fine and luscious, about 10 μm (0.0004 in) in diameter. About 2,000 to 3,000 cocoons are required to make 1 pound of silk (0.4 kg). At least 70 million pounds of raw silk are produced each year, requiring nearly 10 billion cocoons.