BUTTERFLIES AND MOTHS 



323 



On account of its short-lived existence, the cabbage butterfly (like all 

 lepidopterous insects) is able to subsist upon a food which is free from 

 nitrogen, i.e., on sweet vegetable juices. (There are even insects which in 

 their fully developed condition do not feed on anything at all. What do 

 these live on ?) This manner of feeding makes it necessary that the 

 butterfly should be quite different from the sluggish leaf -eating larva. 



1. Being a honey-sucking creature, it must be winged like the bee 

 (which see), and accordingly we find two pairs of wings, both functioning 

 as organs of flight. 



(a) If one of the 

 wings is gently stroked 

 with the finger, it is 

 found to consist of a 

 fine colourless m e m - 

 brane, both sides of 

 which are covered by 

 a loose, easily-remov- 

 able dust. If a piece 

 of the wing be placed 

 under a microscope, 

 this dust will be found 

 to be composed of 

 small regular scales 

 arranged in rows, and 

 overlapping each 

 other like roof-tiles. 

 Each scale is provided 

 at its lower end with a 

 small stalk or pe- 

 duncle, which is sunk 

 into a pit or depres- 

 sion of the wing mem- 

 brane. 



(b) The scales impart to the wing its colour, which is nearly pure white 

 on the upper surface. The tips of the wings are black, and there are 

 two black spots (absent in the male) on the fore-wings, and a black spot 

 on the hind-wings. 



Like a true child of the sun (contrast with crepuscular and nocturnal 

 Lepidoptera) , the white cabbage butterfly is clad in a bright- coloured 

 dress, visible from a distance, and rendering the insect conspicuous to 

 members of its own species and easily distinguishable from other species. 

 As long as it is on the wing this dress does not specially endanger the 



A., PIECE OF A WING OF THE WHITE CABBAGE BUTTERFLY. 

 (Much magnified, to show the Scales.) 



R., Margin of wing ; the scales covering it are very long. The 

 dark scales are of black colour, the light ones white. 



B., A SCALE. (More strongly magnified. ) 



It is fixed by a small peduncle in a depression of the wing 

 membrane (F.). 



