INSECTA, A CLASS OF ARTHROPODS 201 



the winter safely in the protected egg, while most of the adults 

 are frozen to death. The young (nymph), though small, red, 

 and wingless, still resembles the adult in most respects, but as 

 is often the case with the young, the head is disproportionately 

 large. As with all arthropods, they grow by moulting, usually 

 five times, and at each step, develop in size and wings till they 

 reach full growth. The moulting, which takes about half an hour, 

 is followed by rapid growth and formation of a new exo-skeleton, 

 the former one having split along the thorax to allow the exit of 

 the growing insect. It emerges head first but very weak and limp, 

 and often does not survive the process. 



Metamorphosis. In many animals the development from egg 

 to adult passes through more or less distinct stages instead of 

 being a gradual increase in size. Such a life history is called a 

 metamorphosis. 



Among insects these stages may be several in number and the 

 differences between them slight, as in the grasshopper, or there may 

 be four definite and distinct stages, the egg, larva, pupa, and adult 

 as found in the butterfly, for example. The former type is called 

 an incomplete metamorphosis, the latter a complete metamorphosis. 



Economic Importance. The members of the order to which 

 the grasshopper belongs (orthoptera) are with one exception, all 

 harmful to man. Their food is mostly cereal grains or crop 

 plants, which they often destroy over wide areas. Locusts and 

 grasshoppers have been a plague since ancient times. They are 

 often referred to in Scripture and the second chapter of Joel con- 

 tains a very vivid description of the destruction wrought by a 

 swarm of locusts. The only useful relative is the mantis, which 

 is carnivorous and eats other insects, many of which are harmful. 



COLLATERAL READING 



Life History of American Insects, Weed, pp. 67-81 ; Insect Book, Howard, 

 pp. 334-340; Insect Life, Comstock, pp. 70-233; Manual of Insects, 

 Comstock, pp. 104-118; Guide to Study of Insects, Packard, pp. 556-572; 

 Lessons' in Zoology, Needham, p. 48; Textbook of Zoology, Parker and 

 Haswell, Vol. I, p. 584; Textbook of Zoology, Packard, p. 308; Animal 

 Forms, Jordan and Kellogg, p. 117; Animal Life, Jordan and Kellogg, 



