THE ARTHROPODS 385 



place, the pupal case bursts and the perfect insect emerges 

 in full-grown state. 



Insects which have larva and pupa stages do not grow 

 in the winged stage. It is popularly believed that the small 

 flies seen around houses are young ones ; but the truth is that 

 they are adults of small species. 



Many insects live longer in the larval than in the adult stage. 

 Some of the May-flies (also called day-flies and ephemerids) 

 live only a day or two as perfect insects. Vast numbers 

 emerge in the morning, soon lay their eggs, are unable to take 

 food, and perish before the next day. The seventeen-year 

 cicadas (erroneously called " locusts," for this name belongs 

 to grasshoppers) spend the greater part of the seventeen years 

 as larvae attached to roots of trees beneath ground. In the 

 seventeenth summer they come to the surface, soon pass 

 through the pupal stage, and then emerge as perfect insects. 

 A few of them may remain for a number of weeks, but vast 

 numbers lay their eggs in the twigs of trees and die within 

 a few days after becoming adult insects. The larvae which 

 hatch from the eggs deposited in the twigs fall to the ground, 

 burrow, and remain in the soil for nearly seventeen years. 

 A thirteen-year variety occurs in southern states. 



These insects which have complete metamorphosis are 

 regarded as the highest. The complicated life-history has 

 many advantages. The larval or growing stage is often 

 able to conceal itself and to reach food which perfect insects 

 could not get; for example, the larvae of numerous species of 

 beetles, of the cicadas, and of flies. In many cases it is possible 

 for the adult insect to supply food for the larvae; for example, 

 bees supply food to the larvae in the honeycomb, ants feed 

 and care for their larvae, some wasps paralyze other insects 

 by stinging and then place them as food for wasp larvae, and 

 the eggs of many parasitic species are laid in other insects. 

 Still another advantage to some insects is the fact that 

 their larvae easily withstand the winter storms (examples 

 2c 



