Don’t Blame the Bark Beetles
While walking in the woods, you’ve likely encountered a dead log engraved with maze-like squiggles. They may look like magical inscriptions in a secret forest spellbook, but these natural carvings are known as beetle galleries, and the grooves are munched out by the larvae of bark beetles in the subfamily Scolytinae.
“We actually identify bark beetle species based on the gallery pattern,” says Crystal Homicz, a forest entomology PhD candidate at UC Davis. Galleries can be shaped like wings, tuning forks, or the letter E. The native (and very destructive) western pine beetle carves a telltale spaghetti-like squiggle, which researchers call “spaghetti western.” Over 200 different species of bark beetles live in California, most of them native.
Bark beetles get a bad rap because when their larvae nibble all the way around a tree’s inner bark, they cut off its ability to shuttle water and nutrients, and the tree withers and dies. These beetles (at least the native species) are just the last straw—they usually only infest frail, diseased, or already dead trees. But even healthy trees become susceptible when stressed by drought, wildfire, or overcrowding. During the 2014-2017 drought, bark beetles killed over 100 million trees in California, and over the past three decades, more trees in the western U.S. were killed by beetles than by wildfire.
“The size of outbreaks we’ve seen is really just unprecedented,” says Homicz. Scientists use galleries to piece together the histories of beetle outbreaks—and they emphasize that the beetles are not to blame. “People over-demonize bark beetles,” says Homicz. “They’re native here. The forest, when it’s healthy, is adapted to these beetles.”