USEFUL INSECTS 



561 



The carrion beetles and many water beetles act as scavengers. 



The sexton beetles bury dead carcasses of animals. Ants in 



tropical countries 



are particularly 



useful as scaven- 

 gers. Insects 



often do a service 



by eating harmful 



weeds ; thus many 



harmful plants 



are kept in check. 



The "ladybug," 



or ladybird beetle, 



is the natural 



enemy of the 



orange-tree scale. 



It may often be 



found also feeding 



on the plant lice, 



or aphids. 



The ichneumon fly, indirectly, does man considerable good 



because of its habit of laying its eggs and leaving its young to 



develop in the bodies of caterpillars which are harmful to vegeta- 

 tion. Some of the ichneumons even bore into trees in order to 



deposit their eggs in the larvae of wood-boring insects. 



Cochineal and lac. Among the many products of insect origin 



is cochineal, a red coloring matter which consists of the dried 



bodies of a tiny insect, one of the plant lice which live on the cactus 



plants in Mexico and Central 

 America. The lac insect, an- 

 other one of the plant lice, 

 feeds on the juices of certain 

 trees in India and pours out a 

 substance from its body which 

 after treatment forms shellac. 

 Gall insects. Oak galls, 

 growths caused by wasp-like 



tiTuwnell 



The larvae of the ichneumon fly attach themselves to the body 

 of a caterpillar. They grow by sucking the blood from their 

 host and finally they spin cocoons. In this illustration cocoons of 

 an ichneumon fly are fastened to a Spingidae larva which feeds 

 upon the leaves and stems of various plants. 



round 



insect 



monxt-H, 

 Why is the lac insect useful to man ? 



female^ 



