262 NATURE STUDY AND LIFE 



little, and the children will have the more exercise in 

 the fresh air. 



Few species of butterflies do enough harm to require 

 attention on that account. The mourning cloak, Euvanessa 

 antiopa, occasionally does some damage to shade trees, 

 elms, willows, and poplars ; and this is about the only 

 species that lays its eggs in clusters and the caterpillars 

 of which feed close together so that their depredations are 

 conspicuous. Of the entire group the cabbage butterflies, 

 Pieris napi, protodice and, especially, rapcz, are the 

 only serious pests. These are our commonest species, 

 unfortunately. The larvae are the slender green caterpil- 

 lars so numerous on cabbage, cauliflower, other Cruciferae, 

 and also on nasturtiums. Where any of these plants 

 occur we are sure to find, on any warm day between May 

 and October, one or more of these white butterflies laying 

 her eggs. 1 



Space does not permit more than the mention of the 

 names of some of our commonest and more conspicuous 



1 The story of the accidental introduction and spread of what is now 

 the common cabbage butterfly (P. rapes) is of interest as showing the 

 importance of such apparently trifling things. It was brought from Eng- 

 land to Quebec about 1860, probably in ship's supplies or in imported 

 cabbages. In three years it had spread over an area about sixty miles in 

 diameter; by 1871 it covered eastern Canada and the New England states ; 

 ten years later it was common over the eastern half of the continent from 

 Hudson Bay to Texas ; and for some years now it has had possession of every 

 cabbage patch from the Atlantic to the Pacific. In this rapid conquest of 

 the continent our native species of the same genus, which feed on the 

 same plants, have been almost exterminated in many regions where they 

 were once numerous. The writer has counted over five hundred ovules in 

 the ovaries of a newly emerged cabbage butterfly. There are three broods 

 a year in the North and more in the South ; hence a new insect without 

 natural enemies practically owns the earth. 



