190 PTILOTA. 



It is to be observed, however, that the stomach of 

 these insects, like that of the horse, does not possess the 

 power of dissolving these leaves in the most perfect manner, 

 but only of extracting a juice from them. Indeed, this very- 

 circumstance is assigned by John Hunter (Observations on 

 the Animal Economy, p. 221, quoted by Kirby and Spence) 

 as the probable proximate cause for the voracity of herbi- 

 vorous larvae. And hence of the 1206 and a half pounds of 

 leaves actually devoured, 745 pounds are deposited as excre- 

 ment in an indigested state. Hence it is evident, that in 

 comparison with the stomach of the perfect insect, in which 

 state but very little food is in general taken, (and in some 

 cases the insect is even totally destitute of a mouth,) the sto- 

 mach of the caterpillar, and its apparatus for taking its food, 

 must be fully developed ; and this is found to be the case, 

 the stomach occupying a considerable portion of its inte- 

 rior, and the organs of the mouth being very robust. The 

 caterpillar of the goat-moth is three years in arriving at its 

 full size, when it is 72,000 times heavier than when newly 

 hatched: and a silk- worm, weighing, when first hatched, 

 1 -100th part of a grain, consumes in thirty days about 

 60,000 times its primitive weight. 



These particulars may suffice for the voracious powers of 

 individual insects. It is, however, when they have been pro- 

 duced in considerable numbers together that these powers 

 are rendered more widely perceptible ; and^ in fact, become 

 highly prejudicial, as I have already endeavoured to show 

 in the Introductory part of this volume. An instance or two 

 may not, however, be here out of place. Of these, the first I 

 shall mention is the salt-marsh caterpillar of North America, 

 of which an interesting account has been published by Dr. T. 

 W. Harris, in the Massachusetts Agricultural Repository. 

 This insect is the caterpillar of a moth allied to our ermine- 

 spot moths, being the Arctia acria of Fabricius. It is very 



