Probably the first external evidence of the attack of a bark beetle upon living trees with normal green foliage, is the presence of pitch tubes upon the outer bark. These are small, reddish-brown (later becoming grayish-white) masses of pitch and sawdust, which exude from the small cylindrical entrance made by the adult beetle where it bores through the bark to begin its egg tunnel. Each tube represents the entrance of one or more of these beetles. But we must follow these egg tunnels further, to learn how the actual damage is done to the tree. As soon as the bark beetle has made its entrance through the bark, it starts to work up through the live bark and cambium of the tree, forming a tunnel but little larger than the diameter of the beetle, which is known as the egg gallery, These egg galleries vary in shape from straight to winding, and in length from ten to forty inches. As a rule, male and female beetles work together in one gallery, and the eggs are deposited along the sides of the gallery, often in little pockets. When the tunneling and egg-laying process of the adult beetles is completed, their activity ceases, and they are usually found dead at the upper end of their galleries. The larvæ hatch and begin their work by burrowing across the cambium at right angles to the egg galleries. The complete girdling of the cambium layer is not accomplished until the larvæ have completed their work, and the numerous larval galleries, by joining one another, form a complete gallery around the cambium of the tree, thus cutting off the food supply which is made in the leaves of the tree, from the lower portion of the tree, namely the roots. Since the roots cannot live without nourishment, the tree dies. As soon as the larvæ have completed their development they pupate. Later they develop into adult beetles. These adult beetles issue forth in swarms the following spring, to attack new trees.