Q. I have lots of these red and black bugs crawling on my house! Some of them are starting to get inside. Do they bite? What are they?

A. It sounds like you have boxelder bugs. Fortunately, they do not bite and will not cause damage to your home other than maybe some staining if you crush one on the wall or on the curtains. Boxelder bugs can become a real nuisance if they invade in large numbers (which they often do). During the early spring, adult boxelder bugs emerge from their winter hideouts and begin feeding on scrub vegetation. Mating takes place in early summer and female bugs in general will seek out seed-bearing (female) boxelder trees on which to lay their eggs. I say ‘in general’ they seek out boxelder trees (which by the way is in the same family as the maple) because I’ve seen them doing very well on other tree species that were clearly not in that same family. All summer long these insects make their living un-noticed in boxelder, maple, and other tree species. Their feeding causes no significant injury to these trees either, but it is during warm, sunny days in the fall that things ‘get interesting’ with boxelder bugs.

Adult boxelder bugs will leave the trees and will congregate on warmer south or southwest facing sides of homes and buildings. Adult boxelder bugs are strong flyers and may travel several blocks to find suitable winter shelter. If the host tree species are nearby, young nymphs may also crawl to and gather in these same locations. Much like Asian Lady Beetle, boxelder bugs will seek out sheltered areas within the home like attics, walls, or beneath vinyl siding for overwintering sites. They too will ‘wake up’ occasionally during milder winter days and may gather at windows.

Homeowners can take some steps to prevent boxelder bugs from getting inside by properly installing door sweeps on exterior doors, caulking cracks around window and door frames, and having good fitting door and window screens. Sealing any openings where pipes, and utility wires enter the structure may also help. Now while these procedures are worthwhile and effective at reducing the amount of insects potentially entering the structure, some types of home construction (especially vinyl clad homes) really need a supplemental exterior insecticide treatment applied early in the fall.