FOOD OF INSECTS. 387 



Mr. Sheppard in great abundance living upon the dried 

 Cantharides (Lytta vesicatoria) of the shops. On the 

 other hand, Necrophorus mortuorum^ which subsists on 

 carcases, and many other carnivorous species, will make 

 a hearty meal of a putrid fungus ; Ptinus Fur devours in- 

 differently dried birds or plants, not refusing even to- 

 bacco ; and from the impossibility that one of a million 

 of the innumerable swarms of gnats which abound in 

 swampy places, particularly in regions which but for 

 them would be lost to sensitive existence, should ever 

 taste blood, it seems clear that they are usually contented 

 with vegetable aliment. Indeed the males, as well as 

 those of Tabanus of which even the females readily im- 

 bibed the sugared fluid offered to them by Reaumur 2 , 

 never suck blood at all ; so that they must either feed on 

 vegetable matter, which in fact I have observed them to do, 

 or fast during their whole existence in the perfect state. 



Though insects, generally considered, have thus a 

 much more extensive bill of fare than the larger animals, 

 each individual species is commonly limited to a more 

 restricted diet. Many both of animal and vegetable 

 feeders are absolutely confined to one kind of food, and 

 cannot exist upon any other. The larva of (Estrus Equi 

 can subsist no where but in the stomach of the horse or 

 ass, which animals therefore this insect might boast with 

 some show of reason to have been created for its use 

 rather than for ours, being to us useful only, but to it 

 indispensable. The larvae oiSyrphus Pyrastri (Musca, L.) 

 according to De Geer eat no other Aphis but that of the 

 rose b . Most Ichneumons and Spheges prey each upon 



» Reaum. iv. 280. h De Geer,vi. 112. 



2 c 2 



