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 (Carabz) will 
destroy bed-bugs if shut up in the places which thesé inju- 
rious insects infest. 
Here, again, we see the practical utility of the study of 
Natural History in allits 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 Harpa- 
lus calliginosus, Agonoderus pallipes, 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 
