CHAP. CI. 



ULMA'CEIE. U'lMUS. 



1387 



1234. 



segments bearing two rows of spines directed backwards. Before the larva 

 becomes a pupa, it spins a strong web, intermixed with particles of wood, 

 which constitutes its cocoon (/>) ; in some instances the larva changes to a pupa 

 under ground. Infg. 1233., e, f, g, h, and i are representations magnified 

 of the spines upon certain of the abdominal segments : c represents the 4th 

 abdominal segment seen laterally ;/, three of the basal row of spines ; g, three 

 of the hinder row of spines ; and It, three of the basal 

 row of spines of the 9th abdominal segment. Fig. 

 1234. represents the jaws, or mandibles, of the larva, 

 with which it cuts its way through the wood : in this 

 figure, a is the mandible ; b is the labrum, or upper 

 lip ; and c shows the clypeus. These mandibles are 

 formidable-looking instruments, each having the ap- 

 pearance of a sort of chisel, with a toothed edge. The perfect insect {d mjig. 

 1233.) has dark grey wings, clouded with dark brown, and streaked with black. 

 The imago belongs to the class of insects that fly by night, and it appears about 

 the end of June. The female lays but one course of eggs, but these generally 

 amount to 1000 in number, and are always deposited at the base of the trees; 

 whence the caterpillars penetrate the bark, wherever they can find the easiest 

 entrance. The eggs are small, in proportion to the size of the imago; and the 

 caterpillar, which grows to a large size, is said to remain in the larva state three 

 years. The large size of the larva, Samouelle observes, compared with the small- 

 ness of the egg, strengthens this idea, and prepares us to expect that it would be 

 likely to consume a great quantity of wood in the progress of its growth. The 

 smell of the larva is so strong, as to be easily perceived by persons passing near 

 trees infested with it. {SamoueUc.) The green woodpecker preys upon these 

 caterpillars, and its stomach, on dissection, has an intolerable stench. The prin- 

 cipal kinds of tree which the cossus feeds on are, the elm, the alder, the oak, the 

 ash, the walnut, the beech, the lime, and some kinds of willow and po{)lar. 

 The larvae devour the liber, or inner bark, making long galleries in the 

 wood, like the insects that attack the pear tree (see p. 886.), and finally 

 destroying the tree. Many remedies have been proposed ; but that of Latreille 

 apjiears to be most approved of in France. This consists in surrounding the 

 base of the tree, where it has been observed that the females always deposit 

 their eggs, with a thick coating of a mixture of clay and cow-dung, which the 

 insects cannot penetrate. For further inform- 

 ation respecting this insect, see Gard. Mag., 

 vol. xii. p. 464. The fourth enemy of the elm 

 tree is tlie scolytus. The S. destructor Oliv. 

 is generally considered by far the most inju- 

 rious ; but it is assisted in its ravages by 

 another species, the S. armatus. 



Scolylus destructor. The female insect 

 {fig. 1235., in which a is the natural size, 

 and d the insect magnified), about July, bores 

 through the bark, until she has reached the 

 point between the soft wood and the inner 

 bark; she then forms in the latter a vertical 

 channel, usually upwards, of about 2 in. in 

 length, on each side of which she deposits her 

 eggs as she advances, to the number of from 20 

 to 50 in all. It appears probable that, after do- 

 ing this, she dies, without making her way out 

 again, as she may be often found dead at the 

 end of the channel. About September, the 

 larvae are hatched ; and they commence feed- 

 ing upon the matter of the inner bark (r), at 

 the edge of the channel {b), and, in a very 

 slight degree, on that of the soft wood opposite ; advancing, as they {ci:\\, ui a 



1235 



