48 THE BOOK OF BRITISH BUTTERFLIES. 



appearance. On the other hand, many members of the 

 spring brood have the black tip of the fore-wings much 

 powdered with white scales. This butterfly has been 

 known to cross the straits from France in large numbers. 



P. rapae, Linn. (Small Garden White or Small 

 White) (Figs. 27 to 31), so closely resembles P. brassicce 

 in colour and markings that, did we not know it in 

 any other than the perfect state, we might be inclined 

 to look upon it simply as a small variety of its larger 

 relative, especially as they are on the wing together, 

 and haunt similar localities. It equals, if not exceeds, 

 P. brassicce in the damage it does to cabbages and so 

 forth, and like that butterfly is given to migrating at 

 times in large numbers ; indeed, we find that on 5th 

 July, 1846, a tremendous flight crossed the straits from 

 France to Dover in so thick a mass as to darken the 

 air as they passed. About the middle of the present 

 century rapa made its appearance in Canada, where it had 

 previously been unknown. Of course, we can hardly 

 suppose that its wings carried it there : it was doubtless 

 unwittingly transported by human agency in the egg or 

 chrysalis state, unless indeed it was knowingly introduced 

 by some experimental entomologist. 



Most butterflies only fly in the sunshine, but the 

 Small White is not quite so fastidious in this respect ; it 

 occasionally flies, as do its congeners, when the weather 

 is somewhat dull, and even, it is said, after sunset, while 

 it is usually the first on the wing in the morning and the 

 last to retire in the evening. 



Several varieties have been noticed, among them one 

 in which the ground-colour of the wings is a bright yellow. 

 The dark markings, too, are subject to much variation in 

 size and intensity, sometimes being almost or quite absent, 

 especially in the spring brood, while in the brood that 



