Insects in relation to Man 341 



and the abundant supply of some cultivated plant, 

 through the labours of the husbandman, directly 

 encourages the rapid increase of such destructive 

 kinds. Caterpillars of moths and sawflies, Leaf- 

 beetles and their grubs, Aphids and Scale-insects, 

 devour the foliage or suck sap therefrom, leaving it 

 brown and parched ; grubs of Click-beetles and of 

 Crane-flies gnaw at the roots, while the solid wood 

 is riddled by the tunnels of boring-grubs. The 

 damage thus done by insects may be so serious 

 that the only possible remedy is the burning of 

 the plants attacked, in order to stop the further 

 spread of the plague. Sometimes, however, the 

 application of poisonous solutions to the leaves, or 

 of lime to the roots, is found effectual in checking 

 insect-ravages. It is almost needless to point out 

 that a knowledge of the habits and life-histories 

 of injurious insects is of the greatest value to the 

 cultivator who has to fight against them. And it 

 must not be forgotten that he finds allies in those 

 predaceous and parasitic insects which devour the 

 vegetable-feeders. The numbers of the destructive 

 caterpillars are kept down by the ichneumon-grubs, 

 while the grubs of Hovering-flies, Lacewing-flies 

 and Ladybird-beetles, prey upon aphids and coccids. 

 A specially destructive species of coccid accidentally 

 imported several years ago from Australia into 

 California has been largely held in check by the 

 deliberate introduction of a ladybird beetle (fig. 1 1 6), 

 its natural enemy (198, 199, 20l). 



As mentioned in the opening pages of this chapter 

 a number of insects of various orders have taken up 

 their abode in human dwellings, and many of these 

 are highly injurious to stored food and wearing 

 apparel, as well as to furniture and wood-work. 

 The ravages of some tropical Ants and Termites in 



