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 con- 

 tiguity, but both worked hard at the gallery, as did a 

 third and a fourth which he afterwards introduced; 

 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 {Jllhurnum). 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 

 {Tom'icus tijpogrcqolms, Latr.), so called from its 

 tracks resembling letters, amounted to above a million 

 and a half in the Hartz forest. It appears there pe- 

 riodically, 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 



* Boanet, Observ. eur les Insectes, vol. ii. p. 425, 



