1162 THE BUTTERFLIES OF NEW EXGLAND. 



abundant itj everywliorc noticed. In tliis latter instance commercial 

 agencies are amply sufficient to explain the introduction of this butter- 

 fly into our country. It is, however, an insect dependent upon a group 

 of food plants which forbid its passage into the tropics and so will ])revent 

 its spread over more than the north temperate zone. 



It is plain that no butterfly can become cosmopolitan whose caterpil- 

 lar does not feed upon plants found in all quarters of the globe. Yet 

 this is plainly not a sufficient cause for distribution. As a proof of this it 

 may be pointed out that one of the most polyphagous of our butterflies, 

 Jasoniades glaucus, which has an usually extended distribution in North 

 America, where it has several allies, has never become cosmopolitan ; 

 while plants to whicli it might easily adapt itself are found in every quarter 

 of the globe. Moreover, the alliances of the genus are wholly with tropical 

 American forms and its ancestors unquestionably originated in that part of 

 the world. Yet the genus is not found in tropics. Nor has it ever spread 

 to the Old World ; at the same time there are other genera of the same 

 tribe, not distantly related, which do possess members in both the New and 

 Old Worlds, whose food is of a much more restricted range ; such are the 

 genera Iphiclides and Papilio. 



We have another instance of possible cosmopolitanism which is perhaps 

 more remarkable than any of the others, in the spread, \nown to be recent, 

 of Anosia plexippus, which feeds only upon Asclepiadaceae, a group of 

 plants found all over the world in temperate and torrid regions. It is 

 remarkable, because Anosia belongs to a section of the subfamily nearly all 

 whose other membei's belong to the Old World, and yet it is in the Old 

 World that it is now achieving its success. In ancient times, some oflTshoot 

 of the Old World type found its way to the new continent, spread and multi- 

 plied, so long a time ago as to have now become differentiated into several 

 different species and genera, one of which, reintroduced through commercial 

 agencies into the home of its forefathei-s, bids fair to rival its ancient allies. 

 Here then we have a butterfly which may yet become as cosmopolitan as 

 Vanessa cardui is to-day, or only less so from its inability to perpetuate 

 itself in regions with severely cold winters. 



I do not find among our butterflies any otiier which seems to me 

 likely to aspire to similar honor. But it may be pointed out that Pieris 

 rapae is by no means so destructive in Europe as is another butterfly of 

 the same gi-oup, Mancipium brassicae, whose caterpillars, being semigrega- 

 rious, are capable of much more mischief. Should this butterfly be trans- 

 ported to America (audits chances of such transportation seem to be equally 

 good with those of Pieris rapae), it would probably outdo the ravages of 

 Pieris rapae and spread as far as it. 



Considering the relative abundance in individuals of the species of Eho- 

 doceridi above that of any other tribe of butterflies, the prevalence of 



