We have received many emails this week about ‘home invasions’ of odd-looking bugs. In each case, the culprits were boxelder bugs. Although easily recognized as adults, the partially mature phase (nymphs) can be unfamiliar.
Nymphs and adults aggregate in large groups, especially on light-colored homes with a warm-facing side. The concern for damage on ornamental or fruit trees is low. Rather, these are considered a nuisance pest. The sheer and sudden numbers of them is what causes calls to come in.

FOR MORE INFO:
https://pnwhandbooks.org/node/6798/print
http://ipm.ucanr.edu/PMG/PESTNOTES/pn74114.html