FOOD OF INSECTS. 225 - 
Lepisma sacchavina (the common “ wood” or “sugar fish”) in a pill-box.. 
containing only a few grains of magnesia, found it, to his great surprise, 
alive and active in June, 1833, after this protracted confinement, without 
food, of two years." 
In some cases the very want of food, however paradoxical the proposi- 
tion, seems actually to be a mean of prolonging the life of insects. At 
least one such instance has fallen under my own observation. ‘The aphidi- 
vorous flies, such as Sceva Pyrastri, &c., live in the larva state ten or 
twelve days, in the pupa state about a fortnight, and as perfect insects pos- 
sibly as long, the tele 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, [ found, to my great astonishment, alive three 
months after; and it actually lived until the June following without a par- 
ticle 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 regularly 
undergone its metamorphoses, which is as extraordinary a prolongation 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 tubercles 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 favour the hypothesis of some physiologists, who contend that 
every organised being Hes a certain portion of irritability originally im- 
parted 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 insensi- 
bility as that with which our larva purchased the prolongation of its 
existence, 
After this general view of the food of insects, and of circumstances con- 
nected with it, I proceed to give you an account of some peculiarities in 
their modes of procuring it. 
1 Entom. Mag. i. 526. 
2 Not having ever met with another specimen, I am unable to say 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. t. 7. f 1—3.). Its 
shape is oblong-oyal, 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 aculei or teeth ; three or four minilar 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. 
sega beret elevation is also placed in the middle of the back of each 
ent, 
Q 
