244 SCALE-INSECTS, BARK-LICE, MEALY-BUGS. 
The different kinds of lace-wings (Fig. 198) are also so 
fond of such food that they always congregate upon infested trees, 
where their larve, well equipped for their murderous work, make 
havoc, especially among the plant-lice. 
Among flies we also possess a large number of very useful 
insects. Some of them are shown in Figs. 199, 200. In this 
case the larvze are the active cannibals, eating immense numbers 
of the defenseless lice. 
Fig. 200.—Syrphus-fly destroying grain-louse: Adult Fly; a, larva from side, 
showing the wrinkled appearance; b, from above; c, pupa. After Smith. 
Many other beings, such as spiders and mites are not slow 
to utilize such food as plant-lice and scale insects. 
Among birds we have also a large number of friends, which 
eat both the adult insects as well as their eggs. It is a pleasure 
to watch in midwinter the active tit mouse, running up or down 
the trunks of trees, investigating every crack in the branches as 
well, to discover the minute winter-eggs of lice and other insects 
hidden in such places. It is a pity that such useful beings do 
not receive the protection they so well deserve. It is a good thing 
for fruit-growers and farmers that these and other useful birds 
bring up their families so far north that boys with slings, or 
would-be-sportsmen with their deadly guns, can not destroy these 
