260 FOOD OF INSECTS. 



In some cases the very want of food, however paradoxical the proposi- 

 tion, seems actually to be a mean of prolonging th? life of insects. At 

 least one such instance has fallen under my own observation. The 

 aphidivorous flies, such as Scava Pi/rastri, he, live in the larva state ten 

 or twelve days, in the pupa state about a fortnight, and as perfect insects 

 possibly as long, the whole term of their existence in summer not exceed- 

 int^ at the very utmost six weeks. But one^ which I put under a glass 

 on the 2d of June, 1811, when about half grown, and, after supplying it with 

 Aphides once or twice, by accident forgot, I found, to my great astonishment, 

 alive three months after ; and it actually lived until the June following with- 

 out a particle of food. It had, therefore, existed in the larva state more than 

 eight times as long as it would have lived in all its states, if it had regu- 

 larly undergone its metamorphoses, which is as extraordinary a prolonga- 

 tion of life as if a man were to live 560 years. It is true that its existence 

 was not worth having even to the larva of a fly. For the last eight 

 months it remained without motion, attached by its posterior pair of tuber- 

 cles to the paper on which it was placed, manifesting no other symptoms 

 of life than by moving the fore part of the body when touched, and 

 replacing itself on its belly if turned upon its back. But this was quite 

 enough to prove it still alive. I can attribute this singular result to no 

 other circumstance than its having been deprived of a sufficient quantity 

 of food to bring it into the pupa state, though provided with enough for 

 the attainment of nearly its full growth as larva. Possibly the same 

 remote cause might act in this case, as operates to prolong the term of 

 existence of annual plants that have been prevented from perfecting their 

 seed ; and it would almost seem to favor the hypothesis of some physiolo- 

 gists, who contend that every organized being has a certain portion of 

 irritability originally imparted to it, and that its life will be long or short 

 as this is slowly or rapidly excited — no great consolation this for the 

 advocates for fast-living, unless they are in good earnest in their affected 

 preference of a " short life and a merry one ;" though it must be admitted 

 that they would have the best of the argument, were the alternative such 

 a state of torpid insensibility as that with which our larva purchased the 

 prolongation of its existence. 



After this general view of the food of insects, and of circumstances 

 connected with it, I proceed to give you an account of some peculiarities 

 in their modes of procuring it. 



The vegetable feeders have, for the most part, but little difficulty in 

 supplying their wants. In the larva state they generally find themselves 

 placed by the parent insect upon the very plant or substance which is to 

 nourish them ; and in their perfect state their wings or feet afford a ready 

 conveyance to the banquet to which, by an unerring sense, they are 

 directed. All nature lies before them, and it is only when their numbers 



1 Noi having ever met with another specimen, I am unable to saj' of what precise species 

 of aphidivorous fly it is the larva ; nor can I find a figure of it, though it approaches near 

 to one given by De Geer (vi. l. 7. f. 1—3.). Its shape is oblong-oval, length about four 

 lines, and color pale red sprinkled with black. Each of the seven or eight segments wiiich 

 compose the body projects on each side into three serrated flat aculei or teeth ; three or four 

 similar but smaller aculei arm the head ; and two, much larger than the rest, the anus, one 

 on each side of the usual bitid protuberance which bears the respiratory plates. A bifid 

 tubercular elevation is also placed in the middle of the back of each segment. 



