480 THE BUTTERFLIES OF NEW ENGLAND. 



almost everywhere" in India, though he adds that "it is decidedly rare in 

 Calcutta." In the Alps of Europe this insect flies to the snow level ; but 

 in North America, although it maybe regarded as one of the commonest 

 butterflies in the elevated central district, it is most abundant at a level of 

 seven or eight thousand feet. Lieutenant W. L. Carpenter and others 

 have never found it above the timber line ; but Dr. Packard has taken it 

 on Arapahoe Peak, between eleven and twelve thousand feet, and on Pike's 

 Peak from eight thousand feet to within five hundred or a thousand feet 

 from the summit. Professor F. H. Snow has also taken it on Pike's 

 Peak, and the late Mr. J. D. Putnam at the height of 12,500 feet east of 

 Berthoud's Pass. 



Boisduval states that it is much rarer in America than in Europe ; but 

 my experience has been quite the opposite and is confirmed by Doubleday's 

 remark (Gen. diurn. Lep., i : 204) ; "I have never seen it so plentiful in 

 Europe as I have in the United States, especially in Ohio, where I have 

 seen literally tens of thousands on the thistles by the roadsides." In 

 Egypt I found it far more abundant than in Europe. 



There is no spot in New England Avhere it may not be found at certain 

 seasons in abundance. It is an occasional visitor to the barren summits of 

 the White ISIountains, but nowhere in New England is it so abundant as 

 in Nantucket. 



Irregularities of appearance. ''In England and on the continent of 

 Europe," says Trimen (Rhop. Afr. austr., 121) "cardui sometimes 

 appears in great abundance, and then, perhaps for several seasons, will be 

 uncertain in appearance and restricted to particular localities. I ha-se not 

 heard of this irregularity of appearance being noticed in other parts of the 

 world." This is, however, the universal testimony of observers in Amer- 

 ica, and is probably due to the action of parasites. It was one of the 

 first phenomena that drew my especial attention to butterflies. This but- 

 terfly, indeed, is one of the best subjects of study for those who wish to 

 investigate the causes of irregular apparition ; and only such as spend 

 much time in the field can hope to solve the problem. A close observa- 

 tion of the comparative abundance of the butterfly for several consecutive 

 years in the same locality, accompanied by an attempt to rear hundreds of 

 the caterpillars (selecting only those which are nearly full grown, and 

 recording the proportion of healthy and infested ones) , will probably show 

 whether the attack of parasites is a vei'a causa. In New England it was 

 noted as very common in 1878, then very scarce until 1884 when it was 

 extremely common, and equally so over a very wide territory, causing 

 great alarm among the farmers in Manitoba (Can. ent., xvi : 177,211) lest 

 it should be injurious to some of their crops. In 1885 it was again 

 scarce in New England, abundant again in 188(3, and in 1887 rarely seen. 



This irregularity of appearance is sometimes due to immigration from 



