PHASES OF ANIMAL LIFE 



result of migration. I was at first inclined to think, 

 till John Lewis Childs told me, they had become 

 suddenly numerous on Long Island. This fact seems 

 to exclude the idea of migration from some other 

 part of the country. Some parasite, some plague — 

 ehipmunk smallpox, or cholera — may have kept 

 their numbers down for years, when suddenly the 

 enemy vanishes and the race recovers its lost 

 ground. 



These vicissitude?, these ebbs and flows, probably 

 run all through the life of nature about us and we 

 observe them not. I know an asij-tree by the road- 

 side that year after year, early in the season, lost 

 part of its foliage by some form of leaf-blight. Surely, 

 I thought, that tree is doomed; then there came a 

 season when the blight did not appear, and it has 

 not appeared since. A few years ago the elm-beetle 

 threatened to destroy all our elms here od the Hud- 

 son; then it met with a check and seems now to have 

 gone out entirely. A species of forest-worm denuded 

 the sugar maples in large sections of Delaware 

 County, and spread like fire from one wood to 

 another, and grew more and more devastating; then 

 a parasite, a species of ichneumon-fly, took a hand 

 in the game, and in one season the tide ebbed and 

 has never returned. 



A year or two later another species of forest-worm 

 appeared in the same section of the country and 

 stripped the beeches; in midsummer the woods were 

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