60 INSECTS INJURIOUS TO VEGETATION. 



The northern Brenthus inhabits the white oak, on the trunks 

 and under the bark of which it may be found in June and 

 July, having then completed its transformations. The female, 

 when about to lay her eggs, punctures the bark with her slender 

 snout, and drops an egg in each hole thus made. The grub, 

 as soon as it is hatched, bores into the solid wood, forming a 

 cylincMcal passage, which it keeps clear by pushing its castings 

 out of the orifice of the hole, as fast as they accumulate. 

 These castings or chips are like very fine saw-dust; and the 

 holes made by the insects are easily discovered by the dust 

 around them. When fully grown, the grub measures rather 

 more than an inch in length, and not quite one tenth of an inch 

 in thickness. It is nearly cylindrical, being only a little flat- 

 tened on the under side, and is of a whitish color, except the 

 last segment, which is dark chestnut-brown. Each of the first 

 three segments is provided with a pair of legs, and there is a 

 fleshy prop-leg under the hinder extremity of the body. The 

 last segment is of a horny consistence, and is obliquely hol- 

 lowed at the end, so as to form a kind of gouge or scoop, the 

 edges of which are furnished with little notches or teeth. It is 

 by means of this singular scoop that the grub shovels the 

 minute grains of the wood out of its burrow. The pupa is 

 met with in the burrow formed by the larva. It is of a yel- 

 lowish white color; the head is bent under the thorax, and the 

 snout rests on the breast between the folded legs and wings ; 

 the back is furnished with transverse rows of little thorns or 

 sharp teeth, and there are two larger thorns at the extremity of 

 the body. These minute thorns probably enable the pupa to 

 move towards the mouth of its bmTow when it is about to be 

 transformed, and may serve also to keep its body steady during 

 its exertions in casting off its pupae skin. These insects are 

 most abundant in trees that have been cut down for timber or 

 fuel, which are generally attacked during the first summer after 

 they are felled ; it has also been ascertained tiiat living trees 

 do not always escape, but those that are in full vigor are rarely 

 perforated by grubs of this kind. The credit of discovering 

 the habits and transformations of the northern Brenthus is due 

 to the Rev. L. W. Leonard, of Dublin, New Hampshire, who 



