The mountain pine beetle, a native resident of the forests of western North America, is a bark beetle that bores through the bark of mature pine trees to lay its eggs. The attack of the beetle introduces a blue fungus into the tree's tissues. This fungus blocks the tree from repelling and killing the beetle with its sticky sap. In the process, the fungus also prevents the flow of water and nutrients in the tree.
Eventually, the joint effort of the fungus and the beetle kill the tree, causing its needles to turn a characteristic red. Over time, these needles fall to the ground.
Normally, the mountain pine beetle attacks old or weakened trees, removing them from the forest and making room for new growth.
In the past few decades, mountain pine beetle populations have skyrocketed in an epidemic that is threatening the forests of British Columbia, Canada. Cold winter conditions usually kill off many of the beetle's offspring, keeping populations in check. However, the warmer winters of the past decade have drastically increased beetle survival rates and increased the range of suitable beetle habitat. Further aiding the beetle's spread, increasing occurrences of hot, dry summers stress the pine trees, lowering their defences against attack.