38 MISSOURI BOTANICAL GARDEN BULLETIN 



and the bag is promptly attached to a twig. Additional layers 

 of silk are spun within the bag, forming a cocoon, and here 

 the transformation to the pupal stage takes place. In about 

 three weeks after the cocoon is formed the male moth emerges 

 from the base of the bag and flies about seeking the female. 

 The female moth never leaves the bag entirely, although the 

 head emerges from the lower end. Fertilization takes place 

 within the bag, after which the female gradually works her 

 way back into the chrysalis, which she then nearly tills with 

 eggs. After accomplishing this, the female forces her body 

 through the opening in the bag, falls to the ground, and dies. 



Damage. — While the chief damage from this worm is, of 

 course, the defoliation of the tree, an investigation of the effect 

 of the constriction of twigs by the bag worm, published in the 

 Seventeenth Report of the Missouri Botanical Garden, by Dr. 

 Hermann von Schrenk, showed that the pressure exerted by 

 the silken bands on twigs of coniferous trees was sufficient to 

 cut off the food supply and that practically no growth took 

 place in the twig on the sides below the bands. The portion 

 of the twig above the band continued to grow for a consider- 

 able period, but that ultimately considerable damage might 

 occur in coniferous trees seemed to be probable. In the hard- 

 wood trees investigated, with the exception of the locust, the 

 pressure of the band was never great enough to obstruct the 

 passage of elaborated food material. The strength which some 

 of these bands showed was very considerable. The growth 

 energy exerted by the twig, necessary to burst the band, of 

 course varied xery much with the strength of the individual 

 band, but actual measurements showed that as high as 162 

 atmospheres was exerted in one ease and it is probable that 

 in many cases at least from 30 to 40 atmospheres pressure 

 was produced. 



Collecting the Bags.— Since the eggs of the caterpillar are 

 carried over the winter in the bag, the collection and destruc- 

 tion of these bags before the time of hatching is the most 

 natural method which suggests itself of eradicating the worm. 

 On small trees, which can be thoroughly gone over with the aid 

 of a short ladder or by the use of a light pole pruner, such a 

 method is recommended, provided all of the bags can be re- 

 moved. However, unless this can be accomplished for all the 

 trees, both large and small, over a very considerable area, re- 

 sults may be more harmful than beneficial, for the reason that 

 at the time the eggs of the bagworm are destroyed, the natural 

 enemies of the caterpillar are likewise obliterated. Various 

 flies which breed within the bag of the bagworm are parasitic 

 upon the caterpillar and. under favorable conditions, are a 



