114 STATE HORTICULTURAL SOCIETY. 



feeds and thrives upon almost all variety of deciduous trees and 

 shrubs, and often proves a serious orchard pest. 



The development and habits of the insect are peculiarly interesting. 

 During the month of May, in the latitude of St. Louis, tiny dark cater- 

 pillars appear from many of the bags that may be seen in winter hang- 

 ing from the twigs of trees. Almost their first activity is to begin the 

 formation of a case or cover for the hinder part of the body. The pro- 

 cess is described by Dr. Riley, in a popular account of the insect in his 

 first Missouri report, as follows: 



"They crawl onto a tender leaf, and, attached by their anterior feet, with 

 their tails hoisted in the air, they spin around themselves a ring of silk to which 

 they soon fasten bits of leaf. They continue adding to the lower edge of the ring, 

 pushing it up as it increases in width, till it reaches the tail and forms a sort of 

 cone, as represented at ^r in the figure . As the worms grow they continue to in- 

 crease the size of their bags from the bottom, until they become so large and heavy 

 that the worms let them hang instead of holding them upright as at first." 



The silk which forms th«» foundation of the case is of a dingy pale 

 brown, and is so closely woven as to be almost as firm as parchment, 

 and so strong and tough that it cannot be pulled apart with the fingers. 

 The outside is always ornamented with bits of leaves, twigs or what- 

 ever substance is convenient, partly as a disguise. 



In spite of their voracity the worms grow quite slowly and do not, 

 attain their full size until the latter part of July or the first of August. 

 During the four molts or changes of skin they cease feeding for two 

 or three days, retiring within and closing up their bags, after first 

 attaching them in some secluded position. When shed the old skin is 

 pushed out through the small end of the bag, which is always left open 

 for the voiding of the frass. The head and thoracic joints of the larva, 

 which are the only parts ever exposed, are of a horny texture and 

 marked in brown and white, as represented in the cut. The part 

 enclosed in the case is of a dingy white color, somewhat bristly and 

 with a faint stripe along each side. There are none of the pro-legs, or 

 false legs, under this part of the body that most caterpillars possess. 

 Until 'full grown the bag-worms wander but little, and do not leave the 

 tree or shrub on which they were hatched unless the supply of food 

 fails ; but as the time arrives for the first transformation they become 

 very active — crawling from branch to branch, not infrequently dropping 

 upon the clothing of the passer-by, or upon animals, by whom they are 

 unknowingly transported to different localities. As Prof. Riley says, 

 " a wise instinct urges them to do this, for did they remain on one tree, 

 they would soon multiply beyond the power of that tree to sustain 

 them, and would in consequence become extinct." The " wise instinct " 

 also teaches them that they have no other means of reaching "fresh 



