The main attacker in question is the mountain pine beetle, a shiny black insect no longer than one-third of an inch. Its diminutive size belies its power to fell entire forests. In late summer, adult beetles fly from the yellow- to red-needled trees they grew up eating, and seek out large-diameter (meaning older) live trees in which to lay their eggs. The beetles tunnel under the bark, often sending chemical signals that attract more beetles. Each pair lays about 60 to 75 eggs, most of which will hatch. When they do, the larvae burrow deeper into the tree to hide for the winter, producing an alcohol that serves as an antifreeze. The larvae feed in the spring and pupate in the early summer, exiting the trees in late July to start the cycle again. They usually have a one-year life cycle, but warmer seasons have stretched it to two in some places, biologists say.