THE LEPTDOPTERA 



291 



of these insects are very common but are of no importance economically. One 

 species here departs from the general rule as to the food of Lepidoptera, its larva 

 being carnivorous and feeding on plant lice. Unfortunately it is not common 

 enough to be very beneficial. 



Some of the species in this family have more than one generation each year 

 and the adults of tlie two generations are so different that until one kind was 

 bred from eggs laid by the other they were supposed to be different species. 

 Difference in color, markings or both, may therefore be correlated with the season 

 of the year, and insects having two different forms according to the season, 

 present cases of what is called seasonal dimorphism. 



Fig. 310. — The Monarch {Danaus archippus Fab.), natural size. {Original.) 



Family Danaidae. — This small family is of interest in the United 

 States mainly because it includes one of our largest and widely distributed 

 butterflies, the Monarch {Danaus archippus Fab.). This is common 

 in nearly all parts of the country and has a striking way of sailing about 

 in the air. The ground color of the wings is tawny brown marked 

 with black lines along the veins, and broad black borders containing 

 white spots (Fig. 310). The caterpillars feed upon milkweed and are 

 greenish-yellow with black cross-bands and a pair of soft, fleshy projec- 

 tions on the back a little behind the head, and another pair not far from 

 the hinder end of the body. The pupa (chrysalis) is usually attached to 

 the plant and is about an inch long, stout, bright green with golden dots. 



Though the Monarch breeds in the Northern States during the 

 summer, it appears to come from the South each spring, and in the fall 

 multitudes often gather and fly southward together. Whether they 



