334 



FOOD OF INSECTS. 



it may be laid down as a general rule, that almost all insects 

 in this state eat much less than in that of larvas. The yo- 

 racious caterpillar, when transformed into a butterfly, needs 

 only a small quantity of honey ; and the gluttonous maggot, 

 when become a fly, contents itself with an occasional drop or 

 two of any sweet liquid. 



While in the state of larvae the quantity of food consumed 

 by insects is vastly greater in proportion to their bulk than 

 that required by larger animals. Many caterpillars eat daily 

 twice their weight of leaves, which is as if an ox, weighing 

 sixty stone, were to devour every twenty-four hours three 

 quarters of a ton of grass — a power of stomach which our 

 graziers may thank their stars that their oxen are not en- 

 dowed with. A probable proximate cause for this voracity 

 in the case of herbivorous larvae has been assigned by John 

 Hunter, who attributes it to the circumstance of their sto- 

 mach not having the power of dissolving the vegetable mat- 

 ters received into it, but merely of extracting from them a 

 juice. ^ This is proved both by their excrement, which con- 

 sists of coiled-up and hardened particles of leaf, that being 

 put into water expand like tea ; and by the great proportion 

 which the excrement bears to the quantity of food consumed. 

 From experiments, with a detail of which he has favoured 

 me, made by Colonel Machell of Beverley on the caterpillars 

 of Euprepia Caja, he ascertained that, though a larva weigh- 

 ing thirty-six grains voided every twelve hours from fifteen 

 to eighteen grains' weight of excrement, it did not increase 

 in weight in the same period more than one or two grains. 

 On the other hand, many carnivorous larvse increase in weight 

 in full proportion to the food consumed, and that in an as- 

 tonishing degree. Redi found that the maggots of flesh-flies, 

 of which, one day, twenty-five or thirty did not weigh above 

 a grain, the next weighed seven grains each ; having thus in 

 twenty-four hours become about two hundred times heavier 

 than before. ^ 



Some insects have the faculty of sustaining a long ab- 

 stinence from all kinds of food. This seems to depend upon the 



1 Obs.on the Animal (Economi/, p. '221. Compare Reaiim. ii. 167. 



2 Redi de Inseciis, 39. 



