32 Insects Injurious to the Elm. 



existence, however, is a very short one, and the female, so soon 

 as her instinct teaches her that the time has arrived for de- 

 positing her eggs, bores again through the thick bark for that 

 purpose, voluntarily quitting the daylight for ever, as she fre- 

 quently dies almost immediately after depositing her last batch 

 of eggs in the dark tunnel, which thus serves at the same time 

 for the tomb of the parent and the cradle of the progeny.* 



The curiously branching tracks of insects of this class have 

 in many cases suggested the name by which different species 

 are distinguished — each having a peculiar method of progres- 

 sion, which, of course, leaves a track of corresponding charac- 

 ter. For instance, the insect of the genus Bostrichus, the larvge 

 of which makes the little branching channels which look like 

 lines engraved on metal, and are marked a in the engraving of 

 injured wood, No. 2, has received the specific name of chalco- 

 graphus, from a term founded on Greek words meaning " an 

 engraver on brass/' Another, the one whose larva makes the 



* I have just received the following additional details respecting the habits of 

 the Scolytus, and the fatal nature of its ravages. These interesting particulars 

 are from a paper recently read before the Entomological Society, by one of the 

 most careful and accurate observers among our English entomologists: — "When 

 the first warmth of spring sets in the perfect insect mates its escape from beneath 

 the bark, by eating its way out ; the female soon after selects a tree for the pur- 

 pose of depositing her ova ; she commences her perforation always beneath a little 

 projecting piece of bark, at the upper end of a crack; she bores onwards and 

 upwards until on the surface of the alburnum, when she ascends direct. The 

 tube thus formed is from two to three and a half inches in length, three-fourths 

 of a line in diameter, and of equal size throughout, except at a short distance 

 from its entrance, where a small cavity is usually found, sufficiently large to allow 

 the perfect insect to turn ; on each side, in small crenules, she deposits her eggs 

 as she advances. If the female insect live to effect her retreat, she closes the' 

 aperture by which she effected her entrance with some plastic material, to prevent 

 the entrance of enemies ; the number of eggs is in proportion to the length of 

 the tube — there are generally sixty to seventy. On bursting their shells the 

 young larvge immediately commence feeding on the last deposits of alburnum. 

 They at first form parallel lines or tubes, which are seen gradually to enlarge and 

 diverge, and are filled with exuvise. Here they continue to feed during the 

 summer, autumn, and winter (if mild) •, when full-grown they form a case, in 

 which they change to the pupa state, and then, at the end of May, or the begin- 

 ning of June, bore their way out through the substance of the bark. . . When the 

 insect greatly abounds, it will perforate the bark of fresh hewn timber ; but I 

 have never found one specimen in an elm whose juices were dried up. Therefore, 

 irrespective of the cause of disease, it must be unanimously granted that an insect 

 which can destroy four square indies of bark by detaching it from the alburnum, 

 must prove highly destructive, and whilst permitted to remain must frustrate 

 any attempt to restore health. When we find a tree dead, with terminal branches 

 profuse and perfect, we certainly, under ordinary circumstances, should not say 

 that tree had died from defective nutrition in the soil ; but that, from some cause or 

 another, it had suddenly, as it were, come to an untimely end ; and such a tree 

 we had in the Gardens (Royal Botanic) . I watched it in its beauty, and in three 

 years saw it cut down and carried away dead. But what a sight met ovx view on 

 removing the bark — the surface of the trunk, as many gentlemen will remember, 

 for I exhibited a piece of it three feet long before this Society (Entomological), 

 was beautifully scored by the lateral tubes of the Scolytus larva, and we reckoned 

 that this solitary tree gave birth to no less than the prodigious number of 280,000 

 perfect insects." 



