Thank you for the help. I am no expert, but according to several websites they like Ash wood. I recently had 1/4 cord of firewood delivered to my garage. The wood is half Oak and half Ash. I assume they are attracted to my heated kitchen floor which is the closest room to my garage. Should I be worried? Move the wood? I'd prefer not to spray something since the wood is for burning (unless someone knows of some type of safe Box Elder deterrent).
"They may form large aggregations while sunning themselves in areas near their host plant (e.g. on rocks, shrubs, trees, and man-made structures). However, their congregation habits and excreta can annoy people, thus they are considered nuisance pests. This is especially a problem during the cooler months, when they sometimes invade houses and other man-made structures seeking warmth or a place to overwinter. They remain inactive inside the walls (and behind siding) while the weather is cool. When the heating systems revive them, some may falsely perceive it to be springtime and enter inhabited parts of the building in search of food, water, and conspecifics. In the spring, the bugs leave their winter hibernation locations to feed and lay eggs on maple or ash trees; aggregations may be seen during this time and well into summer and early fall, depending on the temperature."