ORDER V. NET-WINGED INSECTS. 219 



all kinds of butterflies, mosquitoes, and caterpillars, are 

 delicious morsels for them. 



It is, however, in this their murderous character and 

 rapacious habits that their chief use to man consists ; for, 

 being themselves directly incapable of injuring him, they 

 rid him of insects that are directly capable of annoying him 

 by biting and stinging. Thus, if a few dragon-flies be shut 

 up in a house for only a short time, they will effectually 

 purify it of all flies, mosquitoes, or other troublesome blood 

 suckers, in the same manner as toads, so much despised and 

 trod upon, will destroy whole armies of disgusting cock 

 roaches, and several species of running beetles (Carabi) will 

 destroy bed-bugs if shut up in the places which these inju 

 rious insects infest. 



Here, again, we see the practical utility of the study of 

 Natural History in all its details. How many take measures 

 to drive out of their gardens the harmless toad, ignorantly 

 bringing upon themselves much greater mischief by the ac 

 cumulation of noxious insects which the toads are destined 

 to destroy, and would destroy, if allowed to carry out the 

 benevolent designs of Nature that placed them there. So, 

 also, would many be horrified to find beetles such as Ilarpa- 

 lus calliginosus, Agonoderus palh pes, etc., in their rooms, or 

 beds, even if the latter were infested with that worst of all 

 household pests the bed-bug, and yet the former are harm 

 less, can not bite or sting, and would surely and effectually 

 destroy the latter. 



So, too, the dragon-fly, which may be handled by man 

 with perfect impunity for it can not bite, or sting, or poison 

 him is often a source of terror in a house or garden, where 

 it might be extremely useful in destroying mosquitoes if al 

 lowed to remain. Only a short time ago, while on a visit 

 to a friend in the country, we were much amused to see 

 one of the young graduates of one of our universities terri 

 bly frightened at a large dragon-fly which had entered the 



