INSECTS. 



21 1 



irregular intervals it sweeps through our meadows and grain-fields about 



the time that wheat is beginning to ripen, often rendering it unfit 



the mower or harvest-machine. It proves injurious from Maine to! 



and from the Atlantic to the 100th meridian." It receives its name from 



the armies it forms when on the march from one 



field to another. Very similar in appearance is «^^!~~\ ^ M 



the cotton-worm moth of the southern states, which J^^^H 



feeds upon the leaves of the cotton, causing an im- * 



mense amount of damage, estimated in some years 



at thirty million dollars. ^3^ ^% 



In the silk-worm family we meet almost the \ ^^^pps^ \i& 

 only moths of value to mankind, and even here all ^^\ 



would be regarded as injurious were it not for the FlG - 268 -— Cot 4 n t " b w " r " : '-'-• a ' 1 ' 1 

 silk that some of them produce. Silk is spun by 



every moth that makes a cocoon, but in the great majority it dues not 

 possess the qualities requisite for a textile fibre; it is not strong enough, 

 or it is not easily unwound, while in others the worms are not easily 

 raised ; so that few have economic value. 



The true silk-worm moth is represented in the upper left-hand corner 

 of our plate. It is an inconspicuous cream-colored or light lemon-yellow 

 species which would hardly be suspected as of great value, and yet it 

 undoubtedly stands first among all the insects. It is a native of China, 

 and neither history nor tradition goes back to the time when it was not 

 reared for its silk ; and to-day the moth or the worm is not known in the 

 wild state. 



As this insect is so important, it may be well to follow it more at 

 length than we have done with the other moths. First, there are numerous 

 varieties, each of which have their merits and peculiarities. The • or 



'seed,' may be fastened to the leaves of the mulberry or some other obji 

 or they may be free in some of the varieties. These eg^± have a commer- 

 cial value, and China and Europe import large numbers of them. They 

 are sold by weight; each moth lays from three to four hundred eggs, md 

 it takes on the average forty thousand eggs to weigh an ounce. 



The silk-worm which hatches from the egg is black or dark gray, ft 

 feeds voraciously on the leaves of the mulberry, and rapidly grows until 

 it becomes necessary to change its skin; it then molts, and r< peats 

 operation three- or four times before it is full grown. It now grew g lighter, 

 becomes a translucent pink or amber color, and begins to spin its silken 

 threads. It is now allowed to crawl to the 'spinning-arches.' — bent tw 

 interlaced with broom-corn or dried brush, — where it begins to spin 

 cocoon. The temperature is now kept at about 80°, and the worm first 



