CARNIVOROUS INSECTS 179 



and when this operation is complete the hover-fly larva 

 casts aside the empty skin and turns its attention to another 

 member of the flock. The importance of these insects 

 from the standpoint of the agriculturist can scarcely be 

 exaggerated. " I have seen currant bushes " (writes Dr. 

 Howard) " upon which there was hardly a leaf which did 

 not support a thriving colony of plant lice and which had 

 not become curled and distorted in consequence ; and yet 

 within a few days, while the distortion of the leaves 

 remained, not a plant louse was to be found, but under 

 each leaf instead of the flourishing group of lice was a fat, 

 full-grown syrphus larva which had destroyed all of the 

 previous inhabitants and was now ready to transform." 



The well-known ladybirds feed largely upon aphides, 

 though some of them attack such pests as scale insects 

 and red spiders. The most familiar British species are 

 the two-spot ladybird (Coccinella bipunctata) and the 

 seven-spot ladybird (C, septempunctata). They lay their 

 small, yellowish eggs in groups upon leaves, usually in 

 the neighbourhood of aphid colonies. The dark-coloured 

 larva? are known popularly as " niggers." They are fairly 

 active in their movements, and never fail to destroy any 

 small, succulent insect which may cross their path. 

 When full-grown, the larva suspends itself by the tail 

 from a leaf, and changes to a pupa. 



The Neuropterous snake-flies (Raphidiidce) may also 

 be reckoned among the gardener's friends, for their larvae 

 destroy multitudes of small creatures which lurk beneath 

 the bark of decaying trees, and in like situations ; while 

 the adults are rapacious foes of lesser insects in general. 

 According to Dr. Howard, the larva? of Calif ornian snake- 

 ilies are especially destructive to the caterpillars of the 

 dreaded codlin moth, which they attack after they have 

 spun their cocoons under the loose bark of apple trees. 



