2l6 NATURE STUDY AND LIFE 



subsist on the juices of their host by means of piercing 

 and sucking mouth parts. 



In the Lecaniums, or naked scale insects, the scale is 

 the insect itself. In the majority of species, however, the 

 scale is an armor composed of powdery, waxy, or even cal- 

 careous substance, together with moulted skins, excreted 

 by the insect and beneath which it lives. Several species 



Fig. 92. Branch of Willow Tree killed by Oyster-Shell 



Scale Insects 



(About natural size) 



furnish valuable commercial products, notably the cochi- 

 neal insect, Coccus cacti, from which cochineal and carmine 

 are derived, and Carteria lacca, living on the branches of 

 several tropical trees, from which we get shellac ; but 

 our common species are among the most troublesome and 

 destructive of insect pests. Like the plant lice they mul- 

 tiply with great rapidity, and their scaly coverings tend to 

 protect them from the oily or soapy washes and sprays 

 commonly used to kill insects by contact. 



