GENERAL FEATURES 33 



believe that some species of butterflies have become estabhshcd 

 in this region, as a result of the increased variet}- of plants now 

 living here. 



But whatever the reason may be, the fact remains ; species come 

 and go, forms prevail, and in time disappear; apparently but few 

 things stand immovable. Perhaps for a century or two the move- 

 ment in most species is not observed, and yet, again, other species 

 move with great relative speed, until, for one, I am on the verge 

 of belief that in a thousand years, or in ten thousand (for a few 

 years more or less do not count), the changes in the butterflies of 

 the West Coast will be very great indeed. How or why the 

 changes come can be told only after much study and observation 

 through many years. Certainly, one man, or one generation of 

 men stands no chance of solving the question. The most that we 

 can do is to note down the things as we find them ; and an aggre- 

 gation of these notes after a series of years will afford a distinct 

 step forward in the investigation. 



§ 32. Dry and Wet Se.\sons. 



When extremely unfavorable dry seasons occur, as in 1883, and 

 1898, birds will not nest, or perhaps will build nests but lay no 

 eggs in them ; bees will not swarm ; and butterflies do not properly 

 appear. It is not well known what becomes of the butterfly na- 

 tion in those bad years. Of course, there are many butterflies on 

 the wing, but some kinds do not appear at all, and other kinds are 

 very few in numbers. They must tide over the dry season, in 

 chrysalis, or die. And I think that in good part, they die. 



I have known that sturdy and vigorous butterfly Papilio Zoli- 

 caon to be almost wiped out by a bad and rainy time when they 

 were just at the point of emergence. I was then engaged in get- 

 ting material for the illustration of Zolicaon for Edwards' But- 

 terflies of North America, and had in previous years secured most 

 of the required material, when a wet spring came on, and it rained 

 every day more or less for forty days ; and Zolicaon did not ap- 

 pear at all that year, and it was several years before they came in 

 from the outside, so to speak, so that I could supply the lacking 

 material. This is the reason that a hiatus of seven years appears 

 in Edwards" history of the species, and in the illustrations thereof ; 

 a hiatus never before explained. 



