170 SHADE-TREES IN TOWNS AND CITIES 



on many plants comprising fruit, shade, and ornamental 

 trees. The easiest way to control the insect is to cut out the 

 twigs having the nests of caterpillars and burn them. 

 On large trees where the nests cannot be easily reached, the 

 foliage at the points where the nests are observed should be 

 sprayed with arsenate of lead. There is no necessity for 

 spraying the entire tree, because the insects feed only in 

 the immediate vicinity of the nest as long as there is any 

 thing to eat at that point. The earlier the spraying is done 

 the more easily will the insects be destroyed. 



Bag Worm ( Thyridopteryx ephemerceformis Steph. ) . This 

 insect derives its name from the fact that the larva is pro 

 tected by a bag or case which it carries about as a shelter 

 and in which it undergoes its transformations. In winter 

 these bags are prominent objects on the leafless trees. 



In May, the caterpillars develop, which after working out 

 of the parent sack, at once begin to construct a bag of their 

 own. At first the sack, which is just large enough to hold the 

 insect, is carried upright; but as the larva increases in size 

 and adds to the sack it becomes too heavy and is allowed to 

 hang down, fastened to a twig or leaf by threads of silk 

 when the insect is not actually moving. 



The feeding on the foliage of the tree continues, and 

 when full grown and ready to transform to the pupal stage, 

 the larvae become restless and wander to other trees. When 

 a suitable place is found, the bags are attached to a twig or 

 other support and the pupa is formed. 



In about three weeks the male moth appears. The adult 

 female is wingless and legless. She does not leave her case, 

 but works out of it far enough to permit pairing, then 

 returns into the pupal skin, fills it with eggs, and wriggles 

 out of the bag and dies. The mouth of the bag closes after 



