124 INDIRECT INJURIES CAUSED BY INSECTS. 



This pest was particularly prevalent and caused incalculable mischief, about 

 the year 1665. In the beginning of the last century it again showed itself 

 in the Hartz forests — it re-appeared in 1757, redoubled its injuries in 

 1769, and arrived at its height in 1783, when the number of trees destroyed 

 by it in the above forests alone was calculated at a million and a half, 

 and the inhabitants were tlireatened with a total suspension of the work- 

 ing of their mines, and consequent ruin. At this period these Tomici, 

 when arrived at their perfect state, migrated in swarms like bees into Suabia 

 and Franconia. At length, between the years 1784 and 1789, in conse- 

 quence of a succession of cold and moist seasons, the numbers of this 

 scourge were sensibly diminished. It appeared again, however, in 1790; 

 and so late as 1786 tiiere was great reason to fear lor the few fir-trees that 

 were left.* 



When the sap flows from a tree in consequence of the attacks of the 

 above-mentioned insects, or any other cause ^, it is attended by various 

 'beetles, as Cetonia ain-ata, several NUidulce and Brachyptera, &c., which 

 prevent it from healing ; and if the bark be anywhere separated from the 

 wood, a numerous army of wood-lice, earwigs, spiders, field-bugs, and 

 similar subcortical insects take their station there, and prevent a re- 

 union. 



The seeds of forest as well as of fruit-trees are doubtless subject to 

 injuries from insects ; but these being more out of the reach of observa- 

 tion, have not been much noticed. Acorns, however, a considerable article 

 with nurserymen, are said to have both a moth and a beetle that prey upon 

 them ; and, what is remarkable, though sometimes one larva of each is 

 found in the same acorn, yet two of either kind are never to be met with 

 together.^ The beetle is probably the Curcidio (^Balaninus) glandium of 

 Mr. Marsham, and is nearly related to the species whose grub inhabits the 

 nut. 



Having now conducted you round, and exhibited to you the melancholy 

 proofs of the universal dominion of insects over our vegetable treasures 

 •while growing or endued with the principle of vitality, in their separate 

 departments, I must nextintroduce you to a pest worse than all put together, 

 ■which indiscriminately attacks and destroys every vegetable substance that 

 the earth produces, and which, wherever it prevails, carries famine, pesti- 

 lence, and death in its train. Happily for this country — and we cannot 

 be too thankful for the privilege — we know this scourge of nations only 

 by report. The name of Locust, which has been such a sound of horror in 

 other countries, here only suggests an object of interesting inquiry. But 

 the ravages of locusts are so copious a theme that they merit to be con- 

 sidered in a separate letter. 



I am, &c. 



* Wilhelm's Recreations from Kat. Hist., quoted by Latreille, Hist. Nat. xi. 194. 



2 While attending to the Scohjti infesting the common ehn during the tour in 

 the north of France in 1836, above referred to, I noticed in the liquid matter so often 

 seen constantly oozing from the large ulcers in this tree, a dipterous larva in con- 

 siderable numbers, of which this exudation is evidently the natural food ; and having 

 bred some of them, they produced very minute gnat-like flies, of the genus Cercito- 

 jiogon, probably (but I have not the specimens now at hand to compare with his 

 description) C. flavifrons of Guerin (J[«w. Sac. Ent, de France, iL 1G5.), which he 

 found in a similar situation. 



3 Reaum. ii. 602. 



