THE BAG WORM. 261 



the details of structure is shown at b, iu the same figure. The extensility of the male 

 genitalia, which permits him to reach the female within her bag, is set forth in the 

 foregoing Fig. 99, where the parts aro shown at rest, c and d, and in action b. Fer- 

 tilization being accomplished, the female works her way back within the chrysalis 

 skin and fills it with eggs, receding as she does so toward the lower end of the bag, 

 where, having completed the work of oviposition, she forces, with a last effort, her 

 shrunken body out of the opening, drops exhausted to the ground, and perishes. 

 When the female has withdrawn, the slit at the head of the puparium and the elastic 

 opening of the bag close again, and the eggs thus remain securely protected till they 

 are ready to hatch the ensuing spring. 



Geographical distribution. — The Bag- worm occurs most frequently in the more south- 

 ern portion of the Middle States and in the Southern States, but seems to be absent 

 from the Peninsula of Florida. Within these limits it extends from the Atlantic to 

 Texas, and reaches the less timbered region west of the Mississippi. Northward, it is 

 occasionally found in New York and even Massachusetts, but so rarely and locally 

 restricted that neither Dr. Harris nor Dr. Fitch mention it in their publications on 

 economic entomology. Wherever it occurs it prefers the gardens and parks within 

 or near the cities, being much less abundant in the woods remote from cities. 



Food plants. — The Bag-worm is known to feed on a large number of trees and 

 shrubs, but has a predilection for certain kinds of coniferous trees, notably the red 

 cedar and arbor vitje, and as these evergreens are much less able to stand the loss 

 of their foliage than the deciduous trees, the worms are much more dangerous to the 

 former than to the latter. The hard maples are, as a rule, avoided by the worms, 

 and it is also quite noticeable that they are not particularly fond of oak leaves and 

 those of the Paulonias. The ailanthus trees are also generally exempt from their at- 

 tacks, either on account of the unpleasant taste of the leaves, or perhaps on account 

 of the compound nature of the leaves, the worms fastening their bags to the leaf 

 stems which fall to the ground in fall. With these exceptions,* the worms, when 

 sufficiently numerous, do great damnge to most other kinds of trees used in our 

 cities as shade and park trees. 



Remedies. — In the case of the Thyridopteryx, effective preventative work can be 

 done during the winter-time or when the trees are bare. ^ The bags which contain the 

 hibernating eggs, and which are very easily detected, may then be gathered or pruned 

 and burned. This work may be so easily done that there is no excuse for the increase 

 of this species. Where intelligent action is possible the bags were better collected and 

 heaped together in some open inclosure away from trees, rather than burned. By 

 this means most of the parasites will in time escape, while the young Bag-worms, 

 which will in time hatch and which have feeble traveling power, must needs perish 

 from inability to reach proper food. 



Enemies. — The Bag-worm is so well protected in all its stages that no insectiv- 

 orous bird nor predaceous insect is known to attack it. In spite of the absence of 

 predaceous enemies, the Bag-worm suffers from the attacks of at least six true para- 

 sites, while two others, which may be primary but are probably secondary, are reared 

 from the bags. Three of these are Ichneumonids, viz: (1) Pimpla conquisitor Say 

 (Fig. 100) ; (2) Pimpla inquisitor Say, and (3) Semiteles thyridopterigis Riley (Fig. 101). 

 Of these, the last-named is most abundantly bred, and we have always considered it 

 as the most important parasite of the Bag-worm. The past season, however, we have 

 ascertained that three species of the genus Hemiteles, viz : H. utilis, and two unde- 

 scribed species, are unquestionably secondary parasites, and this renders it quite 

 likely that H. tliyridopierigis may also be secondary, or, in other words, a parasite of 

 one of the true parasites of the Bag-worm. It is a question, however, which only 

 the most careful study, with abundant material, can decide, as the law of unity of 

 habit in the same genus finds many exceptions in insect life. The other parasites 

 are as follows : (4) Chalcis ovata Say. This parasite is a very general feeder on Lepi- 



*The China trees of our Southern cities are entirely exempt from the worms. 



