Box elder bug eggs are small, reddish, oval-shaped eggs laid in clusters on or near box elder trees in spring. Females deposit them in bark crevices and on leaf surfaces, and they hatch in 11 to 14 days. If you’ve spotted these bugs around your home and want to know where they’re breeding, the eggs are the place to start.
What the Eggs Look Like
Box elder bug eggs are red and roughly oval. Females lay them in small clusters rather than individually, tucking them into tight spaces on bark or placing them on the upper surfaces of leaves. The red color makes them relatively easy to spot against gray bark, though their small size means you’ll need to look closely. They’re often compared to other true bug eggs in shape, appearing somewhat flattened and elongated.
Where Females Lay Their Eggs
The primary egg-laying sites are on box elder trees (Acer negundo), which are the bugs’ namesake host plant. Females strongly prefer cracks and crevices in the bark, where the eggs get some physical protection. They also lay eggs on the tops of leaves and occasionally on other nearby objects or surfaces close to host trees.
Box elder trees aren’t the only hosts. These bugs also feed on other maples and occasionally ash trees. But box elders, especially female (seed-producing) trees, are by far the most common breeding site. If you have a large population of these bugs near your home, there’s almost certainly a box elder or similar maple within a short distance.
Timing and Hatching
Egg-laying begins in spring after overwintering adults emerge with warm weather. The females that survived winter in sheltered spots (under bark, in leaf litter, or inside wall voids of buildings) become active, seek out host trees, and start laying eggs. Once deposited, the eggs hatch in 11 to 14 days. The tiny nymphs that emerge are bright red and wingless, gradually developing the black-and-red coloring of adults through several molts.
Depending on local temperatures, box elder bugs can produce up to two generations per year. In warmer climates, a spring generation matures by early summer, and those adults lay a second round of eggs that produces a late-summer generation. This second generation is the one that typically becomes a nuisance in fall, when large numbers of adults seek warm surfaces on buildings and try to move indoors for winter.
They Don’t Lay Eggs Indoors
One of the most common concerns people have is whether box elder bugs found inside the house are breeding there. They are not. Box elder bugs do not breed or lay eggs indoors. Adults that enter homes in fall are looking for a sheltered overwintering spot, not a place to reproduce. If they get trapped inside a basement or attic, they will eventually die without producing offspring.
This is actually useful information if you’re dealing with an indoor infestation. The bugs you see inside during winter or early spring are a finite population. No new ones are hatching behind your walls. You can vacuum them up without worrying that you’re only catching a fraction of a growing colony.
Reducing Egg-Laying Near Your Home
Because the eggs are laid almost exclusively on or near box elder trees, the most effective long-term strategy is managing the trees themselves. Removing female box elder trees (the ones that produce seed pods) from your property eliminates the primary breeding site. If removal isn’t practical, you can reduce populations by spraying nymphs with insecticidal soap or a strong stream of water shortly after they hatch in spring, when they’re concentrated on the trunk and lower branches.
Sealing entry points on your home, such as gaps around windows, doors, utility pipes, and foundation cracks, won’t stop egg-laying but will keep the resulting adults from moving indoors in fall. Caulk and weatherstripping are your best tools here. The goal is to break the cycle at two points: fewer eggs laid near your home in spring, and fewer adults getting inside in autumn.