390 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 



the ground, leaving the root undisturbed. A glance at the broken end sufficed to 

 reveal the mystery, for it was perforated, both vertically and horizontally, by the 

 tubular excavations of a little Scolytid beetle which, in most instances, was found 

 still engaged in his work of destruction. 



At this time the wood immediately above the part actually invaded by the insect 

 was still sound, but a couple of months later it was generally found to be rotten. 



During September and October I dug up and examined 

 V a large number of apparently healthy young maples 

 'J of about the size of those already mentioned, and 

 -■\ was somewhat surprised to discover that fully 10 per 

 I cent, of them were infested with the same beetles, 

 § though the excavations had not as yet been suffi- 

 ^ ciently extensive to afifect the outward appearance of 

 :;'J the bush. They must all die during the coming win- 

 .•; J ter, and next spring will show that, in Lewis County 

 '.•J alone, hundreds of thousands of young sugar maples 

 lir perished from the ravages of this Scolytid during the 

 summer of 1882. 

 Pig. 145. CoHhy^lmjunM^ ^j^^ ^^^^ ^^.^^ constitutes the entrance to the 



excavation is, without exception, at or very near 

 the surface of the ground, and is invariably beneath the layer of dead and de- 

 caying leaves that everywhere covers the soil in our northern deciduous for. 

 ests. Each burrow consists of a primary, more or less horizontal, circular canal, 

 that passes completely around the bush but does not perforate into the entrance hole, 

 for it generally takes a slightly spiral course, so that when back to the starting point 

 it falls either a little above or a little below it— commonly the latter (see figs. 144, a and 

 b). It follows the periphery so closely that the outer layer of growing wood, sep- 

 arating it from the bark, does not average .25™™ in thickness, and yet I have never 

 known it to cut entirely through this so as to lie in contact with the bark. 



F'rom this primary circular excavation issue, at right angles, and generally in both 

 directions, (up and down), a varying number of straight tubes, parallel to the axis 

 of the plant (see figs. 144, a, b, c). They average five or six millimeters in length and 

 commonly terminate blindly, a mature beetle being usually found to extend farther 

 and, bending at a right angle, to take a turn around the circumference of the bush, 

 thus constituting a second horizontal circular canal, from, which, as from the primary 

 one, a varying number of short vertical tubes branch off, and in very exceptional 

 cases these excavations extend still deeper, and there may be three, or even four, more 

 or less complete circular canals. Such an unusual state of things exists from the 

 specimen from which figure 144, d, is taken. 



It will be seen that, with few exceptions, the most important of which is shown in 

 figure 144, d, all the excavations (including both the horizonta Icanals and their verti- 

 cal offshoots) are made in the sap-wood, immediately under the bark, and not in the 

 hard and comparatively dry central portion. This is doubtless because the outer 

 layers of the wood are softer and more juicy, and therefore more easily cut, besides con- 

 taining more nutriment and being, doubtless, better relished than the dryer interior. 



This beetle does not bore, like some insects, but devours bodily all the wood that 

 is removed in making its burrows. The depth of each vertical tube may be taken as 

 an index to the length of time the animal has been at work ; and the number of these 

 tubes generally tells how many inhabit each bush, for as a general rule each indi- 

 vidual makes but one hole, and is commonly found at the bottom of it. All of the 

 excavations are black inside. 



The beetle is subcylindric in outline and very small, measuring but 3.5™™ in 

 length. Its color is a dark chestnut-brown, some specimens being almost black. Its 

 head is bent down under the thorax and can not be seen from above. (See fig. 145.) 



