USEFUL INSECTS 



the smallest known Hymenoptera. They deposit their eggs in the eggs of 

 other insects, particularly those of moths and butterflies, and are so minute 

 that a single butterfly's egg will suffice for the support of several ichneumon 

 larva?. By this means many eggs of the Lepidoptera must be destroyed, 

 and our gardens and crops are thus protected by insects scarcely visible to 

 the naked eye. 



The Hover Flies or Hawk Flies (Syrphidce), belong to the Diptera, in- 

 sects possessing only two wings. They have a peculiar habit of hovering 

 in the air, darting away like an arrow when disturbed, and hovering 

 again at the end of their flight. They are common from spring to autumn, 

 but more especially numerous from July to September. In appearance 

 many resemble bees or wasps, but may be known by the manner of their 

 flight and the number of the wings. 



The female fly deposits a single white egg in a colony of aphides, and 

 the leech-like larva feeds ravenously upon them, sucking the juices and 

 rejecting the empty skins. It is said that a hungry larva will devour a 

 hundred aphides in an hour. When full-fed the maggot fixes itself to a 

 leaf, stem, or other object by the tail, making the attachment by means of 

 a sticky excretion. The pupa is developed within the larval skin, and in a 

 few days the perfect fly emerges. 



Syrphus (Scctva) pyrastri is a fine species of Hawk-fly, whose larva may 

 be found feeding on the aphides infesting Rose-trees. The insect is blackish- 

 blue, with a whitish-grey down ; usually there are on each side of the abdomen 

 three short bands varying from white to golden yellow. 



Another typical species is Syrphus lucorum. It is a pretty insect, somewhat 

 variable in colour and the extent of its markings, but its general colour is black, 

 the thorax being covered with brown hairs, and the base of the abdomen with 

 golden down. 



Many of the genus Volucella are hairy species, strikingly like wasps and 

 bees. Their larva? are short maggots with pointed tubercles on the seg- 

 ments, living in the nests of wasps and bees, where they act as scavengers 



or feed on the larvae of their hosts. 



xlix f 



