140 NATURE SKETCHES IN TEMPERATE AMERICA 



ing larvae are in consequence of their varied diet characterized 

 as polyphagous. This insect is not alone confined to America 

 and England, but is one of the most cosmopolitan of all the 

 butterflies. It is distributed, according to Holland, over the 

 entire world, with the exception of the arctic regions and 

 the jungles of the Congo in Africa. What, may we ask, are 

 the factors conducive to this wide distribution? 



The life of this butterfly, like many others, is exposed to 

 attack by enemies during all the transitional stages, or instars, 

 from the egg to the adult. The eggs, larvse, and pupae must 

 In some way survive the effects of parasitism. It is probable 

 that during the migration and dispersal of this species, the 

 egg and pupa parasites did not follow their host at once, but 

 in time the parasites followed. The butterflies were thus at 

 first allowed to multiply more rapidly in the absence of these 

 enemies. Parasites, by becoming numerous, probably create 

 a scarcity of their own food supply. A sort of equilibrium is 

 finally maintained between host and parasite, growing out of 

 various contingencies. 



An important factor in aiding the distribution of the Painted 

 Lady is the fact that the food plants, upon which the developing 

 larva depend, were well established prior to the distribution 

 of the butterflies. Its predaceous enemies, such as birds, must 

 be checked by some defensive structures, and these are found 

 on the larvse in the form of distasteful branched spines. In its 

 migrations it was necessary to adapt itself to the physical 

 changes of climate incident to the wide ralige of new conditions. 

 The power of flight also, favored by the air currents, aided in 

 this butterfly's dispersal. 



The larva's existence on the thistle may be recognized by 

 the silken web which it uses to cover itself, and also for 

 the purpose of forming a little canopy out of a leaf for protec- 

 tion. Here the thistle spines may give it slight immunity 

 from preying birds. The full-grown caterpillar attains a 

 length of about an inch and a half. Its body is striped with 

 black and interrupted lines of yellow. The head is black and 

 the feet reddish. There are seven whitish branched spines, 

 those behind the first segment being tipped with black; these 

 spines form an armature to the body which is distasteful to 



