254 AGRICULTURE 



upon the surface or substance upon which it rests. This 

 is the case with the grasshoppers, caterpillars, and most 

 other leaf-feeding insects. Where the jaws point forward, 

 it indicates that they are used for catching prey or for 

 boring into wood. Those insects which catch others are 

 as a rule useful and should not be destroyed. The tigef 

 beetles and the ladybirds are two important groups of such 

 useful insects. 



Sucking insects. In the second large group are in- 

 cluded all insects that take their food by sucking. The 

 mosquitoes, flies, butterflies, moths, and bugs are insects 

 of this class. The food of sucking insects is generally 

 either plant sap or animal blood. The butterflies and 

 moths, however, use neither of these foods, but live on the 

 nectar, or sweet liquid, which is formed in flowers. Some 

 adult insects never feed at all. The larvae from which 

 they are developed have stored up so much strength and 

 a surplus of food materials in their body tissues that the 

 adult simply lives upon that reserve. In such cases the 

 adult may have entirely lost the use of its mouth and 

 the parts may not be developed. Such insects are usually 

 short-lived while in the adult stage. Among the mosquitoes 

 only the females suck blood. It is possible for them to 

 live on some other food as well as upon blood. 



Perhaps the most interesting form of sucking mouth is 

 that of the butterflies and moths. All caterpillars have 

 biting mouths. The tongue of the butterfly is often longer 

 than its body. It would be very much in the way if it 

 were not possible for its owner to coil it up like a watch- 

 spring and carry it closely packed away under its head. 



