FOOD OF INSECTS. 399 



food of any kind*. Some insects, not of a predaceous 

 description, are gifted with a similar power of abstinence. 

 Leeuwenhoek tells us that a mite, which he had gummed 

 alive to the point of a needle and placed before his mi- 

 croscope, lived in that situation eleven weeks'^. 



In some cases the very want of food, however para- 

 doxical the proposition, seems actually to be a mean of 

 prolonging the life of insects. At least one such instance 

 has fallen under my own observation. The aphidivorous 

 flies, such as Syrjihus Pyrastri^ &c. live in the larva state 

 ten or twelve days, in the pupa state about a fortnight, 

 and as perfect insects sometimes possibly as long — the 

 whole term of their existence in summer not exceeding 

 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 v/ithout a particle of food. It had there- 

 fore existed in the larva state more than eight times as 

 long as it would have lived in all its states, if it had re- 

 gularly undergone its metamorphoses — which is as ex- 



^ Phil. Trans. 1740, p. 441. I confess, notwithstanding Mr. Baker's 

 general accuracy, that I suspect some mistake here. 



^ Leeuw. Op. ii. 3G3. 



° Not having ever met with another specimen, I am unable to say 

 of what precise species of aphidivorous fly it is the larva, nor ran I 

 find a figure of it, though it approaches near to one given by De Geer 

 (vi. t. 7. /. 1-3). Its shape is oblong-oval, length about four lines, 

 and colour pale red speckled with black. Each of the seven or 

 eight segments which compose the body projects on each side into 

 three serrated flat aculci 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 bifid protuberance which bears the 

 respiratory plates. A bifid tubercular elevation is also placed in the 

 middle of the back of each segment. 



