Bark-Mining Caterpillars. 257 



case with the social miners of the henbane-leaf. Bonnet 

 ejected one of these, and watched it with his glass till it 

 commenced a new tunnel, which it also enlarged with 

 great expedition; and in order to verify the assertion of 

 Keaumur, that they neither endeavour nor fear to meet one 

 another, he introduced a second. Neither of them mani- 

 fested any knowledge of the other's contiguity, 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 (alburnum). Some of these, though small, commit 

 extensive ravages, as may readily 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 typographies, LATR.), so called from its 

 tracks resembling letters, amounted to above a million 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 neighbourhood of London. 



On taking off the bark of decaying poplars and willows, we 

 have frequently met with the tracks of a miner of this order, 

 extending in tortuous pathways, about a quarter of an inch 

 broad, for several feet and even yards in length. The exca- 

 vation is not circular, but a compressed oval, and crammed 

 throughout with a dark-coloured substance like sawdust 

 the excrement no doubt of the little miner, who is thereby 

 protected from the attacks of Staphylinidm, and other pre- 

 daceous insects from behind. But though we have found a 

 great number of these subcortical tracks, we have never 

 discovered one of the miners, though they are very probably 



* Bonnet, ' Observ. sur les Insectes,' vol. ii. p. 425. 



