INDIRECT BENEFITS DERIVED FROM INSECTS. 151 



egg. The common sand-wasp (Ammophila vulgaris} destroys caterpillars 

 of a larger size, and most of the other Vespoid and Sphecoid Hymeno- 

 ptera, viz. Trypoxylon, Philanthns, Larra, &c. assist in this great work. 



Pompilus, to which genus probably several species mentioned by Reaumur 

 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 Catesby (Sphex cceruleus), has been 

 known to seize a spider eight times its own weight. 1 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 benefactors 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! 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. 2 



Grasshoppers are the prey of another sand- wasp, supposed to be the 

 Sphex pennsylvanica 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. 3 



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 larvas 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 Syrphidce), whose grubs are armed with a singular mandible, furnished 

 ike 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 changing 

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



1 Nat. Hist, of Carolina, ii. 105. 



2 Reaura. vi. 282. St. Pierre's Voyage, 72. 



3 Bartram iu Philos. Trans, xlvi. 12ti. 



L 4 



