154 INDIRECT INJURIES CAUSED BY INSECTS. 



Aphis transpiring a waxy substance like filaments of cotton : this is some- 

 times 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 different 

 species of gall-gnats (Cecidomyia) , or occasioned by the puncture and 

 ovi position 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 monstrosities 

 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 hark, with the adjoining alburnum 

 or sap-wood. Amongst the former the larva of a large weevil (Cryptor- 

 hyncJius 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 Lucanida, have a similar appetite ; but the most 

 extensive family of timber-borers are the Capricorn beetles^, including the 

 Fabrlciarn genera of Prionus, Ceramhyx, Lamia, Stenocorus, Leptura, 

 Rhagium, Gnoma, Saperda, Callidium^, and Clytus. The larva of these, 

 as soon as hatched leaves its first station between the bark and wood, 

 and begins to make its way into the solid timber (some of them plunging 

 even into the iron heart of the oak), where It eats for itself fatuous paths, 

 at its first starting perhaps not bigger than a pin's head, but gradually 

 increasing in dimensions as the animal increases in magnitude, till it attains 

 in some Instances to a diameter of one or two inches. Only conceive 

 what havoc the grub of the vast Prionus giganteus must make in a beam ! 

 Perclval is probably speaking of this beetle, when, in his account of 

 Ceylon, he tells us, " There is an insect found here which resembles an 



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 ene- 

 mies 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. 



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



2 See Kirby in Linn. Trans, v. 250. — More than a hundred species of the Capricorn 

 tribe, many of them nondescripts, were collected near Rio de Janeiro by Captain Hancock 

 of the Foudroyant. 



^ The larva of a CaUidium (which Dr. Leach has discovered to be C. bnjuhtm) sometimes 

 does material injury to the wood-work of the roofs of houses in London, piercing in every 

 direction the fir-rafters (in which it most probably took up its residence while they were 

 growing as trees), and, when arrived at the perfect state, making its way out even through 

 sheets of lead one sixth of an inch thick, when they happen to have been nailed upon the 

 rafter in which it has assumed its final metamorphosis. I am indebted to the kindness of 

 Sir Joseph Banks for a specimen of such a sheet of lead, which, though only eight inches 

 long and four broad, is thus pierced with twelve oval holes, of some of which the longest 

 diameter is a quarter of an inch ! Mr. Charles Miller first discovered lead in the stomach 

 of the larva of this insect. \ 



