BARK-MINING CATERPILLARS. 209 



Social Leaf-Miners. 



The preceding descriptions apply to caterpillars who 

 construct their mines in solitude, there being seldom more 

 than one on a leaf or leaflet, unless when two mother-flies 

 happen to lay their eggs on the same leaf; but there are 

 others, such as the miners of the leaves of the henbane {Hyos- 

 cyamus niger), which excavate a common area in concert — 

 from four to eight forming a colony. These are very like 

 flesh-maggots, being larger than the common miners ; the 

 leaves of this plant, from being thick and jnicy, 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 experimenter 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 

 commenced a new tunnel, which it also enlarged with 

 great expedition ; and in order to verify the assertion of 

 Eeaumur, that they neither endeavour nor fear to meet one 

 another, he introduced a second. Keither 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 

 foinid 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 

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



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



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