OF PIERIS RAPAE IN NORTH AMERICA. 65 



there; one has not seen it and saj^s it must be rare or local if there at all ; the has occa- 

 sionally noticed a Pieris, but took it to be P. oleracea (R. S. Williams) ; the other, Mr. 



F. W. Anderson, says he saw none in 1883, one in 1884 and anothei" in 188G. 



1884 

 North of the boundary, according to the report of a four years' resident, the 



insect has not yet reached Regina (N. 11. Cowdry). 



A few words only will suffice for all later statistics. In 1885 it is recorded from Du- 



luth, at the western end of Lake Superior (W. H. Edwards) ; and Mr. David Bruce, who 



has spent the last thi'ee summers in Colorado and has closely watched all white 



1885-6 

 butterflies on the search for some of the rarer forms, met with P. rapae for the first 



time in 1886, seeing a dozen specimens about Denver between August and October. In 

 this same year it apparently made its first advent into the eastern half of Florida. En- 

 quiries, last autumn, of several entomologists residing there, Messrs. Ashmead at Jackson- 

 ville, Hubbard at Crescent City, Mead and Chase in Orange Co., elicited the uniform 

 response that the butterfly had not reached there; but Dr. J. M. Wheaton of Colum- 

 bus, Ohio, writes me that he obtained a single battered specimen about the first of 

 April, 1886, while on a visit to Jacksonville. There is probably, therefore, no state in 

 the Union, east of the Rocky Mountains, where it does not occur, though it has not been 

 reported, to my knowledge, from Mississippi, Louisiana or Arkansas. It is hardly pos- 

 sible that it has not covered nearly or quite the whole of each, though ]Mr. R. d'Ailly of 

 Malvern, Arkansas, writes me that it has not yet reached that place in the centre of the 

 state. 



If now we examine the map upon which these statements have been represented, we 

 shall be struck, I think, by two or three principal points: 1. The more rapid spread 

 of the butterfly, at first, toward the east and southeast until it reached the sea, rather 

 than toward the southwest along the valley of the St. Lawrence. 2. The compara- 

 tively small amount of hindrance mountainous and elevated countries seem to have pre- 

 sented in the early part of its career; indeed, if the first record of its appearance in 

 East Tennessee is correct (and we have excellent authority for it) these would seem in 

 the warmer latitudes to have offered a distinct highway for the movements of the army 

 which tlie curves for 187J:-1877 are meant to show. 3. The favorable influence of 

 colonies on the spread of the pest with the single exception of that at Omaha. 4. 

 The excessively rapid, forward movement toward the west and southwest as soon as the 

 Valley of the Mississippi is reached ; compare, for instance, the five years' advance from 

 Cincinnati, Ohio, to Lawrence, Kansas, or to Bastrop, Texas, and the otherwise rapid 

 five years from central New York to western Ohio, or the five years it took to cover 

 the New England states. 5. The natural limit to its southern extension, as shown 

 by the fact that it can hardly maintain itself at Apalachicola and has not pushed its 

 way into the peninsula of Florida beyond, hardly to, Jacksonville, although it has for 

 ten years been within what would elsewhere be not more than a year's flight away. 



It may here be mentioned, as a fiict noted by every one who has studied butterflies 

 and by many others, that as fast and as flar as Pieris rapae has spread, it has almost 

 exterminated the native white butterflies, both the southern cabbage butterfly, Pontia 

 protodice, which is itself harmful, and Pieris oleracea, which is comparatively innocuous. 

 It is also observed that the second year after the advent of P. rapae is the one in which 



