THE PREDACEOUS INSECTS 169 



A colony of aphides or plant lice offers many oppor- 

 tunities to study the relations of various groups of insects to 

 one another. In such a colony there are forms of winged 

 and wingless aphides as well as several kinds of enemies 

 that attack them. Among the latter are the tiny four- 

 winged parasites, the young and adult ladybird beetles, and 

 the strange Aphis Lions. In addition to these, you can 

 generally find, also, a curious footless grub blunt at one end 

 and sharply pointed at the other, which impales the plant 

 lice one at a time on its pointed end, sucks the lifeblood, and 

 casts aside the empty skins. These are the larvae of the 

 Syrphus Flies (Syrphidae), many species of which in the 

 larval state thus prey upon the aphides. 



The Syrphus Flies are generally a little larger than the 

 common house fly and may be found in abundance visiting 

 flowers in search of pollen and nectar. The 

 mother flies lay their elongated whitish eggs 

 on leaves and bark amid colonies of plant lice. 

 The eggs shortly hatch into the curious larvae 

 that prey upon the aphides. When full grown, 

 the syrphid larvae change to pupae, still upon 

 the leaf or bark, and change again a little later into adult 

 flies. 



FOUR-WINGED FLIES 



The great order of Four-winged Flies Hymenoptera 

 contains several families that may be classed to a greater 

 or less extent in the predaceous group. One of the most 

 important of these is that of the Ants, which are so univer- 

 sally distributed over the surface of the earth. Most of these 

 ubiquitous little creatures have a wide range of food, taking 

 almost anything, living or dead. There is no doubt, how- 

 ever, that they are important foes of noxious insects, de- 



