68 
Psyche 
[June 
gracilis and emerged during several days beginning on 26 
July. 
14. Vanessa atalanta (L.). Two sites of collection of 
larvae were mentioned above (see N. milberti) . In addition 
a single larva was taken on Urtica at Rabbit Ears Pass, 
Routt Co., Colo., on 15 July 1949. In the Boulder Canyon 
clumps a pupa of V. atalanta was found in one of the 
webbed-leaf nests characteristic of V. atalanta. The larvae 
of the three Urtica-feeding Nymphalididae were easily dis- 
tinguishable by their habits : V. atalanta was always in 
snug nests and always solitary; N. milberti was always 
gregarious, although the social groups were much sub- 
divided and dispersed toward the end of development; P. 
satyrus constructed at best very simple nests and was not 
notably gregarious, and in addition the pair of branched 
head-horns and the broad, creamy dorsal stripe were dis- 
tinctive. The V. atalanta larvae were very heavily para- 
sitized by Larvaevoridae, and four minute Chalcidoidea 
emerged (as hyperparasites?) from a pupa. 
15. Vanessa cardui (L.). Many larvae of all sizes were 
found on Cirsium unclulatum (Nutt.) Spreng. [R.C.R.] 
near Spring Gulch, 9 mi. n.w. of Boulder, Colo., on 7 July 
1949 ; two larval webs each contained a dead larva and a 
cocoon of one of the Ichneumonidae. Females of V. cardui 
were seen on 9 July ovipositing repeatedly on Artemisia 
ludovicianus Nutt. var. gnaphalodes (Nutt.) T. & G. 
[R.C.R.] in clearings in the pine woods near Nederland, 
Colo. This being an atypical foodplant, special care was 
taken to be sure that the butterflies were all V. cardui, 
that ova were actually laid, and that the Artemisia was 
always the plant selected. It is not known whether the 
larvae fed and matured on A. gnaphalodes. No thistles 
were found in these clearings. In 1949 V. cardui was un- 
usually numerous in Boulder County as well as elsewhere 
in North America (see Eff, 1950), and these ovipositing 
females were probably second generation descendants of 
immigrants. V. cardui appears to oviposit commonly on 
plants of doubtful adequacy during these great emigrations 
and then to use only Cirsium and other thistles during the 
