INSECTS 



243 



great economic importance are the Hessian fly, the larvae of which 

 feeds on young wheat; the bot fly, which in a larval state is a 

 parasite on horses; the dreaded tsetse fly of South Africa, which 

 is now believed to cause disease in horses and cattle by means of 

 the transference of a parasitic protozoan, much like that which 

 causes malaria in man; and many others. 



Among the few flies useful to man may be mentioned the 

 fcachina flies, the larvae of which feed on the cut worm, the army 

 worm, and various other kinds of injurious caterpillars. 



Reference Books 



for the pupil 



Davison, Practical Zoology, pages 39-52. American Book Company. 

 Herrick, Text-hook in General Zoology, pages 183-186. American Book Company. 

 Farmers* Bulletin. How Insects affect Health in Rural Districts. U.S. Department 

 of Agriculture. 



The Order Neuroptera 



The Dragon Fly. — The dragon fly receives its name because it preys on 

 insects. It eats, when an adult, mosquitoes and other insects which it cap- 

 tures while on the wing. Its large 

 lacelike wings give it power of very 

 rapid flight, while its long narrow 

 body is admirably adapted for the 

 same purpose. The large com- 

 pound eyes placed at the sides of 

 the head give keen sight. Notice 

 the powerful jaws (almost covered 

 by the upper and lower lips). 

 Compare the position of the wings 

 when at rest with those of the 

 grasshopper. The wings in this 

 case are adapted for swift flight. 



The long thin abdomen does not 

 contain a sting, contrary to the be- 

 lief of most children. These in- 

 sects deposit their eggs in the water, and the fact that they may bo often 

 seen with the end of the abdomen curved down under the surface of the 

 water in the act of depositing the eggs, has given rise to the behcf that 

 they were then engaged in stinging something. The egg hatches into a 

 form of larva called a nymph, which in the dragon fly is characterized 

 by a greatly developed lower lip. When the animal is at rest, the 



Dragon fly. 



Notice the long abdomen and large 

 compound eyes. 



