Insects xvhichjeed upon the Wood of Trees. ^65 



Art. VI. Sovie Account, and partly in Sequel to the foregoing Com- 

 munication, of' Four Species of Insect that feed, while in the La?va 

 State, upon the Wood of Trees. By John Denson, junior. 



The log of pear tree wood which Mr. Rivers has supplied is perforated 

 with many channels, various in direction, most of them in figure com- 

 parable, but perhaps not aptly, to a compressed cylinder, and of size about from 

 Ain. to 1 in. wide one way, and about ^in. wide another. The wood is dead, 

 dry, and hard, and the channels seem as if they had been formed a good while. 

 Their great size led me to think that they must have been formed by the goat 

 moth (Cossus Ligniperda Fabricins) in the larva state, when, I believe, it 

 is larger than any of tliose species of insects, when in the same state, which 

 occur in Britain, that are known to feed, in this state, upon the wood of trees. 

 The subsequent acquisition, from Mr. Rivers, of two living insects in the larva 

 state of the species that has perforated the wood of the pear trees has in- 

 duced me to be of opinion that the species is not the goat moth, but, perhaps, 

 the smaller stag beetle (ZJorcus parallelopipedus Stephens), of which an ac- 

 count will be found below. 



Most of the following matter was prepared previously to the acquisition of 

 the living insects from Mr. Rivers; and I wish to advertise the reader of a 

 sentiment that pervaded me while engaged in the preparation of it, that it 

 may account to him for any seeming pedantry or formality that I suppose may 

 be found in the manner of the matter. The sentiment was, the desire to show 

 my younger brother-gardeners something of a specimen of the manner in which 

 the history of insects should be investigated and stated, and this as a con- 

 tribution to the end, which I hold to be greatly desirable, namely, that brother- 

 gardeners should cease to present their ideas, whether facts or conceptions, on 

 insects, in the vague manner in which they have been too wont to do. 



Some preliminary remarks on insects in general. — The following con- 

 siderations, trite though they may be to many, may be useful to those to whom 

 they are not trite. 



The successive generations of every species of insect proceed from eggs 

 borne by female parents, of that species ; and the eggs are brought forth, in 

 most species, in an unhatched state : in some species they are hatched into 

 larvas (JarvcE) or pupas (^pupct) before they are brought forth. Means for an 

 abundant multiplication of the individuals of insects obtain in the great num- 

 ber of eggs which insects bear, and in their instinctive habit of depositing them, 

 or the larvas and pupas brought forth from them, in places suitable for the 

 sustenance and welfare of their young. 



Insectsare remarkable for the amount of their numerical increase; and the 

 following statements, taken from Kirby and Spence's Introduction to Ento- 

 mology, ed. 1826, may serve to give definiteness to thought on this point. 

 " The fertility of insects far exceeds that of birds, and is surpassed only by 

 that of fishes (the sturgeon is said to lay 1,300,000 eggs, and the cod-fish 

 9,000,000). But the number of eggs laid by different species, sometimes even 

 of the same natural family, is extremely various. Thus, the species whose 

 egg is hatched to a pupa before it is brought forth may be regarded as pro- 

 ducing only a simple egg : il^usca meridiana L., a common fly, lays 2 ; other 

 flies, fi or 8 ; the flea, 12; the burying beetle (Necrophorus vespillo), 30; 

 Mayflies (Trichoptera ^.), under 100; the silkworm moth, about 300; the 

 great goat moth (Cossus Ligniperda), 1000; the tiger moth (Callimorpha 

 Cajfl), 1600; some Cocci, 2000, others 4000; the wasp, at least 30,000; 

 the queen bee varies considerably in the number of eggs that she produces in 

 one season : in some cases it may amount to 40,000 or 30,000, or more,"&c. 

 (iii. 89.) 



The states through which insects pass are four : the egg ; the larva (cater- 

 pillar, grub, and maggot, are names for particular kinds of larva); the pupa 



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