398 FOOD OF INSECTS. 



While in the state of larvae the quantity of food con- 

 sumed by insects is vastly greater in proportion to their 

 bulk than that required by larger animals. Many cater- 

 pillars 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 endowed with. A probable proxi- 

 mate cause for this voracity in the case of herbivorous 

 larvae has been assigned by John Hunter, who attributes 

 it to the circumstance of their stomach not having the 

 power of dissolving the vegetable matters received into 

 it, but merely of extracting from them a juice a . This is 

 proved both by their excrement, which consists 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 con- 

 sumed. From experiments, with a detail of which he 

 has favoured me, made by Colonel Machell on the ca- 

 terpillars of Bombyx Caja, he ascertained that, though 

 a larva weighing thirty-six grains voided every twelve 

 hours from fifteen to eighteen grains weight of excre- 

 ment, it did not increase in weight in the same period 

 more than one or two grains. On the other hand, many 

 carnivorous larvae increase in weight in full proportion 

 to the food consumed, and that in an astonishing 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 



1 Obs. on the Animal (Economy, p. 221. Compare Reaum. ii. 167. 



