Elm- destroying Scolyiiis. 367 



also even appears on the outside of the bark in the form of 

 obscure dark-coloured blotches. Of course, accidental wounds 

 which remain unhealed, and the attacks of other burrowing in- 

 sects, have a similar effect in bringing the trees into an unhealthy 

 state, and in rendering them as fit receptacles for visits of the 

 impregnated female, as if the trees had been first perforated for 

 food by the insects in the unimpregnated state. Two other cir- 

 cumstances, also recently observed by M. Audouin, are of suf- 

 ficient interest to be here noticed : the first concerns the careful 

 selection by the female of the situation in which her burrow is 

 to be made into the bark, when preparing to lay the eggs, and 

 which is generally in that part where there is a fissure, whence 

 she is able to complete her task with less labour, and where the 

 orifice is hidden by the rugosities of the bark, so as to escape the 

 notice of parasites ; and the second, having a similar effect, is, 

 that the female, having deposited her eggs, dies in her gallery; but, 

 by a remarkable display of instinct, she ordinarily crawls to the 

 mouth of the burrow, and thus her dead body forms, as it were, 

 a cork stopping up the aperture and preventing the ingress of 

 enemies. But these cares are not sufficiently efficacious ; for not 

 only has Mr. Spence discovered that many of the larvae, and all 

 the pupae, of the scolytus of the elm which he had examined, 

 were infested with a little parasitic vermicle belonging to the 

 genus Vibrio, and occasionally in vast numbers, but, moreover, 

 that the scolytus is also attacked by a small but beautiful parasitic 

 ichneumon, belonging to the genus Bracon, which I captured 

 near Paris, but which is not an inhabitant of this country. 



The larva of the scolytus {,fig. 73. c, natural size; «, magni- 

 fied) is a small, white, fleshy grub, destitute of legs, and bearing 

 a considerable resemblance to that of the nut weevil. The body 

 is curved into a semicircle, and the segments are transversely 

 channeled. The head is horny and smooth, without antennae ; the 

 upper lip {d) is transverse, with the angles rounded, and with 

 short hairs ; the jaws [g) are obtuse and strong ; the under 

 jaws (Z») flat, internally ciliated, and furnished with a very short 

 2-jointed palpus; and the lower lip [f) is produced in the 

 centre, with two very short palpi. The pupa [e) exhibits 

 the general form of the perfect insect, the limbs resting upon 

 the breast. 



According to the recent observations of Drs. Erichson and 

 Ratzeburg, there are two species which have been confounded 

 under the name of Scolytus destructor, differing in the punctation 

 of the elytra and general outline, but more especially in the 

 form of the burrows of the larvae. I believe both these species 

 are inhabitants of this country : but, for the purpose of assisting 

 the investigation, I have added outlines from Dr. Ratzeburg's 

 beautiful work, just published [Die Forst-Insehten ; Berlin, 



