124 



CRABS AND INSECTS. 



FIG. 152. Aphis. 



nal female may be represented in the twelfth generation 

 by one quintillion descendants, all born in a single sum- 

 mer. Upon the approach of cold weather, or from a lack 

 of food, males and females are pro- 

 duced by the viviparous form, and 

 eggs are laid that in the spring give 

 rise to successive broods, as above. 

 Order V. Beetles (Coleopterci). 

 General Characteristics. Insects 

 having their fore-wings thickened, 

 forming horny sheaths, called elytra, 

 or wing-covers for the hinder pair, 

 that are principally used in flight ; 

 mouth-parts adapted for biting ; 

 metamorphosis complete. 



The Girdler (Oncideres). This 

 beetle displays remarkable intelli- 

 gence in providing for its young. 



The eggs are deposited in perforations in the tender 

 brushes of hickory, and, as the young require dead wood 

 to eat, the mother girdles the limb below the eggs with 

 her mandibles, so that it dies by the time the larva 

 hatches. 



Spring-Beetles (Elateridce). These beetles are light- 

 givers (Fig. 153), and when placed upon their backs have 

 the power of spring- 

 ing repeatedly into 

 the air by using a 

 spine situated be- 

 tween the legs. The 

 larvae are known as 

 wire-worms, and feed 

 upon vegetable mat- 

 ter, sometimes re- 

 maining five years 

 in the larval state. The yellow luminous spots are upon 



FIG. 153. A luminous beetle (Pyrophorus 

 noctilucus). 



