These boxelder bugs didn't fly to the building this spring; they were already there. This fall home invader overwintered somewhere in the building (walls, attic, etc.) and spring temperatures are beginning to roust them from their winter barracks. The bugs were clustered as they awaited outdoor temperatures that will support their flight; they were gone from the building as of yesterday.
The bugs Larry photographed had successfully made their way outside, but this is not always the case. Occasionally, they become confused by warm indoor temperatures and find their way into homes and other structures. They don’t bite or represent a threat to anyone or anything inside a structure, but they can be serious nuisance pest as they frantically crawl or fly around looking for a route to the great outdoors.
This is the first report I've received this spring of boxelder bugs emerging from their overwintering sites. However, with the predicted warm-up this week, I'm sure this is just the beginning.
We can also expect other fall home invaders to soon make their spring appearances. These include Western Conifer Seed Bugs (Leptoglossus occidentalis); Multicolored Asian Lady Beetles (Harmonia axyridis); and the notorious Brown Marmorated Stink Bugs (Halyomorpha halys).