ARTHROPODA 



105 



the web-secreting glands of spiders) extend nearly the entire length 

 of the body. The animal swings its head from side to side, hour 

 after hour, carrying a tiny thread of silk across with each vibration 

 of the head. From this cocoon the adult moth hatches in 15 to 20 

 days, lays her eggs and dies. The cocoons that are used for silk are 

 heated to kill the inclosed larvae, for if allowed to hatch they would cut 



FIG. 79. Caterpillar with cocoons of the pupse of ichneumon fly parasites 

 and (above) one of the adult ichneumon flies. The lines indicate natural dimensions. 

 (From Jordan and Kellogg, Animal Life.) 



the silk threads in emerging. Sufficient numbers of cocoons are kept 

 alive and allowed to hatch for breeding purposes. The utmost clean- 

 liness and proper temperatures are necessary for the best results. The 

 white mulberry furnishes the best food for the larvae, though the black 

 mulberry, osage orange and other trees may be used. 



