CLASS INSECT A 



287 



of the moths, and some of the butterflies, form cocoons as protective 

 coverings for the pupae, and the same is true of some other insects, 

 including beetles. A cocoon may be constructed by the cementing 

 together by the larva of the hairs of its own body or objects of various 

 kinds, including grains of sand or bits of vegetation. It may also be 

 made of silk spun by the larva from a secretion formed by silk glands. 



Common orCulex Mwlcxrial or Anopheles Yellow Fever or Aedes 



Fig. ISO. — Comparison of three importtint kinds of mosquitoes, Culex, Anopheles 

 (Sec. 114), and Aedes, showing eggs, larvae, i)upae, and adults. X 2 or 3. {From Melcalf 

 and Flint, "Destructive and Usefvl Insects," after Pieper and Beauchamp, by the courtesy of 

 Scott, Foresman and Company-) Aedes transmits yellow fever. The horizontal lines 

 indicate water level; the stages of each type are in a vertical column. 



The gall wasps, belonging to the order Hymenoptera (hi men op' ter a; 

 G., hymenopteros, membrane-winged), and the gallflies, belonging to 

 the Diptera, are small and rarely noticed, but the results of their work are 

 frequently conspicuous (Fig. 185). They possess an ovipositor with 

 which they pierce plant tissues and deposit eggs. Either poison injected 

 at the time of the laying of the egg or irritation arising from the growth 



