292 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 193 4 



flying in summer farther north. But corresponding differences are 

 found between the early spring and later individuals in butterflies 

 that are wholly southern in their distribution. 



This is well illustrated by the zebra swallowtail {Papilio niar- 

 cellus)^ of which the individuals flying in early spring are very small 

 and very hairy, corresponding to the earliest individuals of the yellow 

 swallowtail {P. glaucus). It is also seen in the blue swallowtail {P. 

 philenor) in which the form found in early spring in the vicinity of 

 Washington is very small and very hairy, with the light spots on tlie 

 upper surface of the wings large and conspicuous. 



These early spring individuals of the blue swallowtail approach 

 more or less closely the individuals of the Calif ornian form {hir- 

 suta). With them there are occasionally found individuals of a 

 tailless form {acavda) that are almost or quite identical with others 

 from the hot lands of Mexico. 



Speaking of butterflies of hot lands and more or less arid regions, 

 it may be mentioned that in all of our western and southwestern 

 swallowtails {Papilio 7'utilus, P. daunus, and P. p^ilumnus) there is 

 on the under side of the fore wings just within the outer border a 

 broad, yellow, tapering band that takes the place of the row of 

 spots seen in the common yellow swallowtail in summer. In the 

 far north, in the high mountains of India and of central Asia, and 

 in the vicinity of Washington in early spring the yellow swallow- 

 tails {Papilio machaon and P. glaucvis) all have this yellow band, 

 just as do the arid country species. 



Speaking of these yellow swallowtails, it is of interest to note 

 that our American yellow swallowtail {P. glaucus) in the far north 

 flies together with the Old World swallowtail (P. machaoyi) both in 

 the region of Hudson Bay and in Alaska. In the region about 

 Hudson Bay the Old World species occurs in a form {hudsonianus) 

 that is scarcely dilferent from the form found in northern Europe, 

 but in Alaska the local form (aliaska) is an offshoot from a group 

 of similar forms living in the Himalayas and in the mountains of 

 eastern Asia. In these two regions the local representatives of 

 the American yellow swallowtail also show considerable differences. 



ANALYSIS OF THE ARCTIC BUTTERFLY FAUNA 



The outstanding and important characteristic of the Arctic archi- 

 pelago, according to Prof. Robert F. Griggs, is its extreme dryness. 

 The annual precipitation in all high Arctitc countries is less than 10 

 inches, a deficiency in rainfall that in lower latitudes would invari- 

 ably mark a desert. Middenclorf long ago described the Siberian 

 tundra as the most extreme desert, and said that it was too dry to 

 be compared with any region familiar to Europeans. 



