390 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 
Tig. 145. Corthylus jninctatissimvs. 
Merriaui del. 
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 op and examined 
:i large number of apparently healthy young maples 
of about the size of those already mentioned, and 
was somewhat surprised to discover that fully 10 per 
cent, of them were infested with the same beetles, 
though the excavations had not as yet been suffi- 
ciently extensive to affect the outward appearance of 
the bush. They must all die during the coming win- 
ter, and uext spring will show that, in Lewis County 
alone, hundreds of thousands of young sugar maples 
perished from the ravages of this Scolytid during the 
summer of 1882. 
The hole which 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 mm in thickness, and yet I have never 
known it to cut entirely through this so as to lie in contact with the bark. 
From 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, 6, 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 brauch 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 lcanals 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 mm 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.) 
