270 NATURAL HISTORY/ [CH. XIX. 



bark of an infected tree begins to appear as if all its 

 crevices were full of a very fine sawdust. The last 

 change of the. insect takes place; and being now 

 winged, it tries to arrive at the external air, for the 

 purpose of propagating its species, and laying its 

 eggs in other trees. Each hole, which now appears 

 as if made with a gimlet, marks the exit of a per- 

 fect insect. In the first instance the voracity of 

 the larvae, and in the second the endeavours of the 

 perfect insects to liberate themselves from the 

 wood, particularly where such attempts are made 

 by almost infinite numbers, soon occasion the bark 

 to fall in large pieces. The consequence is, that the 

 new leaves only make their appearance to wither, 

 and the tree perishes. It is advisable for those per- 

 sons who have elm-trees which are attacked by 

 these animals, to inspect them twice every year: 

 first in summer, when the perfect insect is on the 

 wing ; and secondly in winter, when the trees which 

 are much infected ought to be cut down. Such 

 trees ought, if possible, to be burnt with the larvae in 

 them, or, if this be not convenient, they should im- 

 mediately be subjected to such heat or fumigations 

 as may destroy the larvae, which at this season are 

 near the surface, and therefore not so difficult to 

 kill. To rest content with having cut down the 

 trees without destroying the larvae, or even remo- 

 ving the trunk from the vicinity of sound wood, is, in 

 reality, to do no good at all. In the year 1780, an 

 insect of the same kind appeared in infinite numbers 

 in the pine forests of the Hartz, andVas neglected. 

 In two years afterward whole forests had disap- 

 peared, and, for want of fuel, an end was nearly put 

 to the mining operations of this extensive range of 

 country. 



In 1782 the public attention was excited by the 

 unusual appearance of an infinite number of large 

 white webs, containing caterpillars, conspicuous on 

 almost every hedge, tree, and shrub in the vicinity 



