MINING CATERPILLARS. 239 



leaves of this plant, from being thick and juicy, 

 giving them space to work and plenty to eat. 



Most of the solitary leaf-miners either cannot or 

 will not construct a new mine, if ejected by an ex- 

 perimenter from the old, as we have frequently 

 proved; but this is not the case with the social 

 miners of the henbane leaf. Bonnet ejected one of 

 these, and watched it with his glass till it com- 

 menced a new tunnel, which it also enlarged with 

 great expedition ; and in order to verify the assertion 

 of Reaumur, that they neither endeavour nor fear to 

 meet one another, he introduced a second. Neither 

 of them manifested any knowledge of the other's 

 contiguity, but both worked hard at the gallery, as 

 did a third and a fourth which he afterwards intro- 

 duced ; for though they seemed uneasy, they never 

 attacked one another, as the solitary ones often do 

 when they meet.* 



Bark-mining Caterpillars. 



A very different order of mining caterpillars are 

 the progeny of various beetles, which excavate their 

 galleries in the soft inner bark of trees, or between 

 it and the young wood (Alburnum). Some of these, 

 though small, commit extensive ravages, as may rea- 

 dily be conceived when we are told that as many as 

 eighty thousand are occasionally found on one tree. 

 In 1783 the trees thus destroyed by the printer-beetle 

 (Tomicus typographus, Latr.), so called from its 

 tracks resembling letters, amounted to above a mil- 

 lion and a half in the Hartz forest. It appears there 

 periodically, and confines its ravages to the fir. This 

 insect is said to have been found in the neighbour- 

 hood of London. 



On taking off the bark of decaying poplars and 

 willows, we have frequently met with the tracks of 



Bonnet, Observ. aur leu Insectes, vol. ii. p. 425. 



