26 



ON THE DIFFERENT SPECIES OF HTLESINUS 

 OCCURRING IN THIS DISTRICT. 



By Dr. CHAPMAN, Abergavenny. 



The genus Hylcsin us belongs to a family of the Rhyncopliora, or weevils, 

 named from it the Hylesinid*, also called by some authors the Xylophaga, and 

 classed as a distinct section. 



The Hylesinidre have the head rounded and sunk in a deep socket in the 

 thorax ; the rostrum or snout so characteristic of the weevils is nearly obsolete ; 

 the autennce have a long basal joint, and are more or less clubbed at the ex- 

 tremity, and with never more than ten joints ; the mandibles are very strong and 

 prominent, though short ; the extremity of the tibipe hooked, and the third 

 tarsal joint bilobed ; the larvas are footless grubs. All the species are small, 

 black or duU brown in colour, cylindrical in shape, and especially rounded on the 

 iipiJer surface. 



It is a very natural group, all the species being very similar in appearance 

 and habits ; most of them pass their lives in the inner bark of trees, iu which 

 some of them commit gieat devastations. 



The species of Hylesinus are more rounded than those of the other genera 

 of the Xylophaga. They possess autennse with an oval elongate club, and tibire 

 obsoletely spurred. 



The perfect insect foi-ms a burrow or gallery in the cambium layer of 

 the bark of recently fallen trees, along the sides of which the eggs are deposited ; 

 the larvEe feed in the inner bark during the ensuing months, whilst it stiU 

 retains a modified vitality, and complete their metamorphosis in time to renew 

 the same cycle the ensuing year. The species of Hylesinus form theii- burrows 

 transversely to the fibres of the tree ; most of the other genera of the famUy 

 form them parallel with them. The larv», starting at right angles to the parent 

 burrow, form theirs in the reverse direction or nearly so, their increase in size 

 makes them diverge from each other and produces rather a fan-shaped marking. 



Of the four species of Hylesinus wluch occur in England, one, Hylesinus 

 Olciperda, which is like a little round dumpy Hyksinus crenatus, we will dismiss 

 at once, as I have not succeeded in meeting with it in this district. The two 

 species to which I have dkected most attention, Hylesinus crenatus and 

 Hylesinus Fraxmi, are attached to the ash tree (Fraxinus excelsior). The 

 fourth species, Hylesinus vittatus, is attached to the elm tree, and is fairly 

 abundant in tliis district. It is difficult, however, to say of any species of the 

 Xylophaga whether it is abundant or not, as, however difficult it may be to 

 find it, when found it is almost certain to be in some numbers. Thus, though 

 H. crenatus is a scarce species, I could have taken it last winter in almost 

 unlimited numbers. Hylesinus Fraxini is, nevertheless, an undoubtedly 

 abupdant sjiccics. At this season (Jlay 22) it may be found on any recently 



