78 



ARTHROPODA 



ing the cocoon is then wound off on a reel, and is often 

 found to be more than a mile long. Three thousand 

 cocoons are required to make a pound of raw silk, and 

 about ninety of the cocoon fibers as spun by the worm are 

 twisted together to make a thread of sewing silk. 



The value of the silkworm was dis- 

 covered 1700 B.C. by the wife of the 

 third emperor of China, who is known 

 as the goddess of silkworms. For 

 nearly two thousand years, the Chinese 

 kept the method of obtaining silk a 

 profound secret. The penalty for 

 carrying the eggs out of China was 

 death. In 555 A.D., two Nestorian 

 monks were bribed by the Byzantine 

 emperor Justinian to bring him silk- 

 worm eggs concealed in the hollow of 

 their pilgrim staves. The industry then 

 spread rapidly throughout Europe, 

 and in 1622 reached America, but 

 owing to the high price of labor, the 



na. 76. -snk glands of insect is not cultivated here to any 

 the silk worm. Natural great extent. From twenty-five thou- 

 sand to fifty thousand cocoons are 

 required to produce sufficient silk for a dress. 



The forest tent caterpillar (Clisiocampa disstria) and 

 its cousin, the apple tree tent caterpillar, are the only larvae 

 which spin webs in the trees hi the spring. The larvae 

 break from the egg mass surrounding a twig, in early May, 

 and in a few days construct a tent to protect themselves 

 during the cold rainy weather. They grow to full size in 



