]g6 INDIRECT BENEFITS DERIVED FROM INSECTS. 



rnur as preying on these insects should be referred, has it in charge to 

 keep the number of spiders within due bounds : and some sand-wasps lend 

 their aid. One of these last, mentioned by Caiesby (^Sphex atruleus), 

 has been known to seize a spider eight times its own weight.^ Another 

 species of this genus, which is common in the Isle of France, attacks an 

 insect still more difficult, one would think, to turn to its purpose, the all- 

 devouring Blatta, or cockroach, and is therefore one of the great benefac- 

 tors to mankind. When this insect perceives a Blatta (called there 

 Kakerlac and Cancrelas) it stops immediately : both animals eye each 

 other; but in an instant the sand-wasp darts upon its prey, seizes it by the 

 muzzle with its strong jaws, and, bending its abdomen underneath it, 

 pierces it with its fatal sting. Sure of its victim, it now walks or flies 

 away, leaving the poison to work its effect 1 but in a short time returns, 

 and, finding 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, supposed to be the 

 Sphex pensylvanicn 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.^ 



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 fiies, whose wings resemble the finest 

 lace, and whose eyes are often as brilliant as burnished metals (Hemtro- 

 hius), 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 themselves are furnished with a 

 pair of long crooked mandibles 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 largest; and the individuals of one species clothe themselves, like 

 Hercules, with the spoils of their hapless victims. 



Next in importance to these come the aphidivorous flies (many species 

 of Syrphida), whose grubs are armed with a singular mandible, furnished 

 like a trident with three points, with which they transfix their prey. They 

 may often be seen laid at their ease under a leaf or upon a twig, environed 

 by such hosts of Aphides, that they can devour hundreds without chang- 

 ing their station ; and their silly helpless prey, who are provided with no 

 means of defence, so far from thinking of escaping, frequently walk over 

 the back of their enemy, and put themselves in his way. When disposed 

 to feed, he fixes himself by his tail, and, being blind, gropes about on 

 every side, as the Cyclops did for Ulysses and his companions, till he 



» Nat. Hist, of Carolina, ii. 105. 3 Reaum. vi. 282. St. Pierre's Voyage, 72. 



3 Bartram in Philos. Trans, xlvi. 126. 



