194 ANIMAL FORMS 
Many of this great group of the flies spend their early life 
in the water or other medium acting as scavengers; but, on 
the other hand, numbers attack domestic and other animals, 
and throughout their entire lives are an intolerable plague. 
121. The beetles (Coleoptera).—Owing to the ease of pres- 
ervation and their bright colors, the beetles have probably 
been more widely collected than other insects. Fully ten 
Fie. %6.—Long-horned borer (#7gates). Larva (left-hand figure), pupa, and adult 
insect. 
thousand distinct species are known in North America 
alone. They are all readily recognized by the two firm, 
horny sheaths enclosing the two membranous wings, which 
alone are organs of flight. The mouth is provided with 
jaws, which are used in gnawing. Some prey on noxious 
insects or upon decaying vegetable or animal matter, and 
are often highly beneficial; but others attack our trees and 
domestic animals, and work incalculable damage. 
