INJURING THE LEAVES. 191 



into little, green larvae that feed upon the substance 



of the foliage. In 



about two weeks they 



become full grown 



(Fig. 100, a), when 



they generally leave 



the cabbage plants, 



and, finding Some Fig . im . imported Cabbage Butterfly. Male 



suitable shelter — beneath a board or under the cop- 

 ing of a fence — change to chrysalids (Fig. 100, 6). 

 They remain in this condition about ten days, when 

 they emerge as butterfles, to lay eggs for another 

 brood of worms. The winter is passed in the chry- 

 salis state. There are several generations of larvae 

 each season, the number varying with the climate 

 and latitude. 



This insect has numerous natural enemies with 

 which to contend. • The larvae and pupa? are preyed 

 upon by certain parasitic and predaceous insects, and 

 the butterflies are often captured by insectivorous 

 birds, as well as by a predaceous bug, known to ento- 

 mologists as Phymata ivolffii. The larva? are often 

 destroyed by thousands by a bacterial disease — a sort 

 of insect cholera — that has lately aided greatly in 

 checking the injuries of this pest. 



There are two or three species of native cabbage 

 worms — notably the Southern Cabbage Butterfly 

 (Pieris protodice) and the Potherb Butterfly (P. olera- 

 cea) — closely related and similar to this Imported 

 Worm, that were formerly quite injurious to cabbage, 



