INDIKECT INJURIES CAUSED BY INSECTS, 



177 



lure that attracts the swarms of ants which you may often 

 see travelling up and down the trunk of the oak and other 

 trees. ^ The larch in particular is inhabited by an Aphis 

 transpiring a waxy substance like filaments of cotton : this is 

 sometimes so infinitely multiplied upon it as to whiten the 

 whole tree, which often perishes in consequence of its attack. 

 The beech is infested by a similar one. Some animals also 

 of this genus inhabiting the poplar, elm, lime, and willow, 

 reside in galls they have produced, that disfigure the leaves 

 or their footstalks. Perhaps those resembling fruit, or flowers, 

 or moss, produced by the Aphis of the fir {Aphis abietis^^ 

 the dilFerent species of gall-gnats ( Cecidomyid), or occasioned 

 by the puncture and oviposition of the various kinds of gall- 

 flies ( Cynips), may be regarded rather as an ornament than as 

 an injury to a tree or shrub ; yet when too numerous they 

 must deprive it of its proper nutriment, and so occasion some 

 defect. And probably the enormous wens^ and other mon- 

 strosities and deformities observable in trees, may have been 

 originally produced by the bite or incision of insects. 



Besides exterior insect enemies, living trees are liable to 

 the ravages of many that are interior. These interior feeders 

 may be divided into two great classes — those which bore into 

 the heart and substance of the wood, and those which feed 

 upon the inner bark, with the adjoining alburnum or sap-wood. 

 Amongst the former the larva of a large weevil ( Cryptorhyn- 

 chus lapathi) bores into the wood of the willow and sallow, 

 which thus in time often become so hollow as to be easily 

 blown down.^ The Stag-beetle tribe, or LucanidcE, have a 

 similar appetite ; but the most extensive family of timber- 



1 It is contended by some observers, that besides the honey-dew caused by 

 Aphides, there is another arising solely from a morbid exudation of the saccha- 

 rine juices of trees. This is certainly possible ; but I may observe, that in the 

 course of more than thirty years which I have attended to this subject (seven of 

 them spent on the Continent, where the greater heat might be supposed likely to 

 cause morbid vegetable action,) I have never met with any honey-dew which did 

 not seem to me very clearly referable to Aphides as its origin ; though, from 

 the circumstance of their having been all swept away by the attacks of their 

 natural enemies and other causes, while their saccharine excretion remains on 

 the leaves for weeks in a dry time, and after being moistened by a slight dew 

 may have every appearance of being a recent morbid exudation, and may, even 

 after very copious dews, fall on the ground, a casual observer may often be 

 plausibly led to a different conclusion. 



2 Lewin in Linn. Trans, iii. 1 . Curtis in ditto, i. 86. 



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