72 



ARTHROPODA 



FIG. 65. Photograph of the 

 larva of a tiger swallowtail. 

 Natural size. 



whose life history may be studied 

 to the best advantage in late 

 summer and autumn. The spe- 

 cies was brought from England 

 to Quebec about 1860 in im- 

 ported cabbages. In three years 

 it had spread over an area of 

 sixty miles in diameter. By 

 1871 it was present throughout 

 eastern Canada and New Eng- 

 land. Ten years later it was 

 common from Hudson Bay to 

 Texas, and since 1895 it has 

 been a pest from the Pacific to 

 the Atlantic. 

 The green larvse are found from June to November by 



noting on the cab- 

 bage plants the 



dark shotlike ex- 

 cretions indicating 



the presence of the 



animals. Several 



placed in a box 



and fed daily with 



fresh cabbage 



leaves will within 



a week or two form 



cases of the last 



molted skins and 



change to the pupal 



state, lasting in early summer but a few days, while later 



FIG. 66. Photograph of pupal or chrysalitl case and 

 the black swallowtail that came from it. Two 

 thirds natural size. 



