260 INDIRECT Benefits derived from iNSECfsi 



destructible part of it; and thousands of orifices into 

 the solid trunk are bored by others. The rain thus in- 

 sinuates itself into every part, and the action of heat 

 promotes the decomposition. Various fungi now take 

 possession and assist in the process, which is followed 

 up by the incessant attacks of other insects, that feed 

 only upon wood in an incipient state of decay. And 

 thus in a few months a mig^hty mass, which seemed in- 

 ferior in hardness only to iron, is mouldered into dust, 

 and its place occupied by younger trees full of life and 

 vigour. The insects to which this duty is intrusted have 

 been already mentioned in a former letter (p. 233-4) ; 

 but none of them do their business so expeditiously or 

 effectually as the Termites, which ply themselves in 

 such numbers and so unremittingly, that Mr. Smeath- 

 man assures us they will in a few weeks destroy and 

 carry away the trunks of large trees, without leaving 

 a particle behind; and in places where, two or three 

 years before, there has been a populous town, if the in- 

 habitants, as is frequently the case, have chosen to 

 abandon it, there shall be a very thick wood, and not 

 the vestige of a post to be seen. 



I observed in a former letter, that the devastations 

 of insects are not the same in every season, their power 

 of mischief being evident only at certain times, when 

 Providence, by permitting an unusual increase of their 

 nunibers, gives them a commission to lay waste any par- 

 ticular country or district. The great agents in pre- 

 venting this increase, and keeping the noxious species 



the bark entire, though the wood \va? decayed. Hence wc may probably 

 tjafevi that in that country there are few or none of the burk-boring in- 

 sects. 



