264? INDIRECT BENEFITS DERIVED FROM INSECTS. 



to work its effect ; but in a short time returns, and, find- 

 ing it deprived of power to make resistance, seizes it 

 again by the head, and drags it away, walking backwards 

 to deposit it in a hole or chink of a wall*. 



Grasshoppers are the prey of another sand-wasp, sup- 

 posed to be the Sphex pensylvanica of Linne, a native of 

 North America, each of which in its larva state devours 

 three of a large green species with which its mother has 

 provided it b . 



From none of the imparasitic insectivorous larvae do 

 we derive more advantage than from those which devour 

 the destructive Aphides, whose ravages, as we have seen 

 above, are more detrimental to us in this island than 

 those of any other insect. A great variety of species, of 

 different orders and genera, are employed to keep them 

 within due limits. There is a beautiful genus of four- 

 winged flies, whose wings resemble the finest lace, and 

 whose eyes are often as brilliant as burnished metals 

 (Hemerobius\ the larvae of which, Reaumur, from their 

 being insatiable devourers of them, has named the lions 

 of the Aphides. The singular pedunculated eggs from 

 which these larvae proceed I shall describe when we 

 come to treat upon the eggs of insects ; the larvae them- 

 selves are furnished with a pair of long crooked mandi- 

 bles resembling horns, which terminate in a sharp point, 

 and like those of the ant-lion are perforated, serving the 

 insect instead of a mouth ; for through this orifice the 

 nutriment passes down into the stomach. When amongst 

 the Aphides, like wolves in a sheep-fold, they make 

 dreadful havoc : half a minute suffices them to suck the 



a Reaum. vi. 282. St. Pierre's Voyage, 72. 

 b Bartram in Philos. Trans, xlvi. 12t>. 



