LEPIDOPTERA. 205 



insectivorous birds, this position may serve as a means 



of protection. They transform in silken cocoons, in 



the earth or under leaves or stones. Fig. 156, a, 



is the pupa of the male ; 



b^ that of the female, also 



seen in Fig. 155, ^. /^, top 



view of anal tubercle of 



pupa, enlarged. The 



"spring canker-worm," 



Paleacrita vernata (Fig. 



157. ^; b. egg, enlarged, F>g- ^57- 



natural size shown in the small mass at side ; c, one 



ring of larva, side view ; d, the same, dorsal view) , 



is more abundant than the "fall canker-worm," and 



may be distinguished from it by not having prop-legs 



on the eighth ring. These moths come out of the 



ground in the early spring.^ 



NOCTUID.E. 



The " northern army-worm " moth, Leucania uni- 

 puncta, Haw. (Fig. 158), is so called because the 

 larvae (Fig. 159) often march in vast numbers. This 

 manner of travelling, however, is abnormal, as stated 

 by Riley,- the insects being usually sedentary in habit, 

 and not marching unless their numbers are large, and 

 the food supply of the region too small. Genera- 

 tion after generation of these caterpillars may live 

 in a given district, feeding upon grass until one or 



1 For further information on the Phalaenidae, see " Packard, 

 Monograph of Geometrid Moths," Hayden's U. S. Geol. Sur- 

 vey, Vol. X., 1876. 



2 Third Rep. U. S. Ent. Com., 1880-82, Chap. VI., p. 109. 



