The western pine beetle is an aggressive dark beetle that attacks and can kill ponderosa and coulter pines that are greater than 6 inches in diameter. The bugs eat the inner bark, while also transporting a fungus into the water-conducting wood to effectively clog the system and kill the tree.
The beetle is found throughout the western United States, causing the most damage in California. The species often attacks trees weakened by disease, drought, fire, old age and wind damage. While the beetle performs the ecological function of recycling nutrients to encourage germination and new tree growth, areas with many weak trees can experience population surges in the beetles that trigger mass attacks powerful enough to overwhelm numerous healthy trees.