224 INSECTS INJURIOUS TO FOREST AND SHADE TREES. 
In the longer ones two beetles (probably the two sexes) were usually found, and fron 
two to four perforations attorded means of ingress and egress. The lowest perforation, 
which is the one by which the beetle first enters and commences its furrow, is often 
found closed or ‘‘ blocked up” by the dust and débris thrown down by the excavator 
in the progress of the work. The second perforation is generally 1 or 2 inches above 
the first. I failed to discover whether it is made by the second beetle for the purpose 
of ingress or by the first beetle. The third and fourth perforations are in a nearly 
direct line above the other two, and are probably made from within outwardly, but 
for what purpose is uncertain. In one instance the two beetles were found at work 
making these perforations, boring through from the inner surface of the bark. In one 
instance the third was less than half an inch above the second, so that there would 
seem to be no particular necessity for it. 
The eggs of the insect are deposited along both sides of the upper part of the fur- 
row. They lie close together, almost or quite in contact with each other. When the 
larvee emerge from the eggs they begin to feed upon the soft cambium and to work 
their way under the bark at right angles to the main furrow. They are at first so 
minute and work so close together that they make no distinct furrows, but seem rather 
to devour entirely a very thin layer of the cambium; but as they increase in size they 
begin gradually to form distinct furrows and to take directions more divergent from 
each other, and from their original course. In this way colonies from contiguous fur- 
rows at length run together, and in time the whole is surrounded by their ‘multi- 
tudinous pathways, and the death of the tree is accomplished. Great care is taken 
by the parent beetles to keep their furrows separate. No instance was observed in 
which they ran together. In one instance the course of a furrow was changed to 
avoid running into the lateral furrows of a colony of larvie just above. No furrows 
were found in the tree more than 10 or 12 feet from its base, thus indicating that the 
attacks are made upon the lower part of the trunk. The attacks are not made simul- 
taneously. Some of the furrows in this tree were scarcely more than an inch long, and 
evidently had been just commenced. Others were fully excavated and contained eggs, 
and in others still the larvie had hatched and commenced their work, but in none were 
they fully grown. In another tree, a few rods distant from the first, the attack had 
evidently been made earlier in the season, for the larvee were further advanced in size 
and the bark on one side of the tree was well loosened, though, strange to say, the 
other side of the trunk was comparatively unharmed. Iwas ynable to discover why, 
in this instance, the attack was limited to one side of the trunk. It is pretty evident, 
therefore, that the trees are attacked all along during the months of June and July, 
and possibly as late as August. I suspect, also, that the parent beetle, after having 
established a colony in one place, may emerge from her furrow to repeat the opera- 
tion in another place, either in the same trunk or in a different one, but this I was 
not able to ascertain definitely. 
A whitish fungus, Polyporus volvatus Pk., scarcely larger than a hickory nut, occurs. 
in considerable abundance on the trunks of spruces killed by this beetle. The myce- 
lium of the fungus grows beneath the bark, and the external plant is connected with 
it through the perforations made by the insect. Hence this fungus becomes a con- 
spicuous indicator of the track of the beetle and tells the tale of its destructive power. 
In a subsequent report, the thirty-first, Mr. Peck thus refers to the 
injuries by bark borers of the balsam fir: 
The wood of the balsam is of little value for lumber, owing to the small size of the 
tree. It contains resin and burns freely, but with a crackling noise. The smoke is. 
yery penetrating and iritating to the eyes. Nearthe summits of the mountains, how- 
ever, it is almost the only available wood for camps and camp-fires. The bark of this. 
tree furnishes the well-known ‘‘Canada balsam,” a clear viscid resin of considerable 
repute in medicine and much used in mounting objects for the microscope. The resin 
is obtained from small vesicles or ‘‘ blisters” in the bark. 
