THE CLASSIFICATION OF INSECTS 



167 



one family, the Sialida, of which the large dobson-fly or hell- 

 grammite is the best known species, are passed in the water of 

 streams or ponds, but the members of all the other families 

 are terrestrial through all their life. Of these the ant-lions, 

 whose larvae make small pits in loose soil in which to catch 

 prey, and the aphis-lions, lace- winged flies and snake-flies, 

 whose sharp- jawed larvae feed on such small defenseless in- 

 sects as aphids and codling moth larvae, are more or less famil- 

 iar and may be counted as beneficial insects. There are no 

 seriously injurious insects in the order. 



FIG. 78. Pit of ant-lion, and, in lower right-hand corner, pupal sand- 

 cocoon, from which adult has issued, of ant-lion, Myrmeleon sp. 

 (About natural size.) 



Order Mecoptera. The order Mecoptera includes a few 

 little-known insects called snow-fleas and scorpion-flies. The 

 mouth-parts are of biting type, and are elongated to form a sort 

 of short, blunt beak. The metamorphosis is complete. Most 

 of these insects are probably predaceous in habit, feeding on 

 other small insects, and thus perhaps doing good, but some 

 take only animal food found dead. The curious snow-fleas, 

 Boreus, are minute, black, leaping creatures that appear on 

 snow in winter time, and in summer live on tree trunks or in 



