204 



NORTH AMERICAN INSECTS. 



in the month of July, during which they pass through at 

 least three transformations — from the egg to the caterpil- 

 lar, and then to the pupa, which is brownish gray, with 

 some golden spots. This butterfly is frequently found in 

 Europe, where it is also a native ; but there it is called 

 Mars, because some have discovered marks upon the wings 

 which are thought to possess some similarity to certain in- 

 struments of war. 



The Thistle 'Btjttebfly (Va?iessa cardui), Fig. 51, some- 



Figure 51. 



The Thistle Butterfly. 



times appears in such large numbers that their larvis devour 

 not only the leaves, but also the blossoms of the thistle and 

 Jjurdock. As soon as one of these caterpillars issues from 

 the egg it draws the points of two leaves together, fastens 

 them with a silky thread, conceals itself therein, and eats 

 the substance of it, until it attains its growth, which is one 

 and a half inches long, when it is ready to metamorphose 

 into a cocoon, from which the perfect insect proceeds in 

 about two weeks. The whole process of its three trans- 

 formations occupies only four weeks — as it remains an egg 

 one week, a caterpillar another week, and a cocoon two 

 weeks. Thus, three or four generations may appear in one 

 summer. The cocoon is generally of a golden-yellow color, 



