Western Box Elder Bugs tend to group up in the fall as they look for a protected place to overwinter. Sometimes, that place is a house or building. Like many other true bugs, the wings of box elders form a characteristic “X” pattern on their backs …but it’s hard to see from this photo since the majority of the bugs pictured here are still nymphs, with short, stubby black wings (you can see a few in the mix if you look closely). These insects primarily feed on the leaves and seeds of box-elder, maple, and ash trees, using their long “beak” to suck the juices. In spring, you will see similar swarms as they emerge.
Photo by Kim Annis on 9/23/20 near Missoula, MT