BUTTERFLIES OF MONTANA. 149 



Genus THANAOS, Boisduval. 



Butterfly Antennae have a moderately large club, curved, bluntly 

 pointed. The palpi are porrect, the third joint almost, concealed in the 

 hair of second. All dark in color. 



PERSIUS' DUSKY-WING, Thanaos persius, Scudder. 



Fig. 108. Thanaos persius, from Helena. Fig. 109. Thanaos persius. 



Butterfly Expanse, 1.2 to 1.4 inches, 30 to 35 mm. Upper surface 

 dark brown with a row of small white spots before the apex of the fore- 

 wings, and a single one posterior to these. On the fore wings there is a 

 transverse pale band just beyond the middle of the wings, but this band 

 is not as well defined as in T. lucilius, which is found in the eastern part 

 of the United States. Hind wings more of a reddish brown than the 

 fore wings, with two rows of indistinct ochraceous spots near the outer 

 margin, and a spot at the end of the cell in typical specimens. 



Underside of the females grayish brown, the apical portion of the fore 

 wings gray; the white hyaline spots are repeated, and both wings have 

 two marginal rows of whitish spots. The males are darker than the 

 females. 



The species is subject to great variation, some specimens being light 

 and others dark in color. Holland says "There is scarcely any positive 

 clue to the specific identity of the insect except that which is derived 

 from the study of the genital armature of the male, which is a micr- 

 scopic research capable of being performed only by an expert in such 

 matters." 



Early Stages The caterpillar feeds on willow and poplar. 



Distribution From New England across to the Pacific, southward as 

 well. In the state it has been taken by Elrod at Missoula and in the Mis- 

 sion Mountains; by Douglas and Smith at New Chicago; by Cooley at 

 Bozeman, by Brandegee at Helena, and by Coubeaux at Big Sandy. 



