The mountain pine beetle, smaller than a grain of rice, plays an important role in forest renewal. This black, hard-shelled bug attacks and kills weakened pine trees enabling the growth of saplings. So why is it considered a pest? Mountain pine beetles are killing forests not just trees. The hot, dry summers and mild winters of recent years have led to an explosion in the population of this tiny insect. There are more mountain pine beetles today than ever before! What's more, a no fire policy has undermined Mother Nature. The forests in western North America are jam-packed with mature pine trees; the favorite food of the mountain pine beetle.