120 THE SCOLYTID BEETLES. 
When the eggs hatch, the minute white grubs or larvae eat their 
way into the soft inner bark, which by this time has commenced to 
die and is in the best condition for their food supply. When the eggs 
are deposited in separate cavities, each larva makes a separate mine, 
but when they are massed along the sides, or placed close together, as 
they usually are, the larvae work side by side and consume all of the 
inner layer of bark until they have progressed some distance, when 
they begin to separate and each larva makes an independent mine. 
While the individual burrow may cross and recross its neighbor, it 
preserves a course of its own and increases in width as its occupant 
increases in size, until the larva ceases to feed. The latter then 
excavates a cavity, either in the bark next to the wood or next to the 
outer dry bark, where in due time it changes to the pupa. Here it 
remains in a semidormant condition until the legs, wing covers, and 
other parts develop. It then sheds its outer skin and becomes an. 
adult winged beetle, soft and yeUow at first, but gradually hardening 
and becoming darker. 
When the individuals of a brood are fully matured in the spring, 
they bore through the inner bark between the transformation cells 
and congregate in the larger common chamber thus formed until it 
is time for them to emerge. They then bore their way out to the 
surface and emerge to fly in search of suitable trees in which to exca- 
vate galleries and deposit eggs. Scarcely anything is known of the 
flight habits, but the beetles probably fly during the evening or at 
night. 
ECONOMIC FEATUKES. 
CHARACTER OF ATTACK AXD INJURY. 
So far as known, tins beetle confines its attack to the spruce in the 
region north of latitude 43°. Toward its southern limit it evidently 
does not occur at altitudes below 2,000 or 2,500 feet, while at latitude 
47° in Maine and in extreme northern Michigan it would be found below 
an altitude of 600 feet. It is rarely found in trees under 10 inches 
in diameter breast high, but prefers those IS inches or more in 
diameter. Whenever it occurs in sufficient numbers to attack and 
kill large numbers of trees the hying beetles within a given locality 
usually concentrate on groups or patches of timber of greater or less 
extent. The trees die from the attack, and when the new broods 
develop they emerge from the dying trees and settle on the living 
timber in another locality, and so on, until all of the matured timber 
is killed. They usually settle on a tree and enter the bark in such 
numbers that there is little chance for its recovery. Their numerous 
egg galleries are extended through the most vital part of the tree 
(the cambium), where the new growth of wood and bark takes place. 
Thus the injury produces a weakened condition of the tree. This is 
