Invertebrates
Box Elder Bug
Boisea trivittata · also called box elder bugs, boxelder bug
A south-facing wall turns nearly black with hundreds of box elder bugs on a warm autumn afternoon, an alarming sight that turns out to be entirely harmless, just a crowd of insects looking for a sheltered place to spend the winter.
Overview
The box elder bug, Boisea trivittata, is a common, harmless true bug found in forest and grassland habitat across much of North America wherever box elder and other maple trees grow. Its dramatic autumn gatherings, bold black-and-red colouration, and complete harmlessness to people and property make it one of the more visually striking yet genuinely unthreatening insects most homeowners will encounter.
A nuisance with nothing to fear
For all the alarm a wall covered in box elder bugs can cause, the species poses no real danger at all, simply seeking a warm, sheltered crack to wait out the winter before returning to its namesake trees in spring.
Status
Least Concern — widespread and abundant across suitable habitat throughout North America wherever box elder and other maple trees grow.
Box Elder Bug: common questions
Is the box elder bug dangerous to people or homes?
No, despite gathering in large, sometimes alarming numbers on sun-warmed walls and occasionally entering homes in autumn, the box elder bug does not bite, sting, or cause any structural damage, making it a harmless if sometimes unwelcome seasonal nuisance rather than a genuine threat.
Why do box elder bugs gather in such large groups?
In autumn, box elder bugs congregate by the hundreds on sun-warmed surfaces, especially south-facing walls, seeking warmth and shelter before winter arrives, a behaviour that often brings large numbers into close contact with homes and buildings.
Why is it called the box elder bug?
This species takes its common name from the box elder tree, a type of maple whose seeds and foliage make up the bulk of its diet, with the insect's distribution across North America closely tracking wherever box elder and related maple trees grow.
How does the box elder bug survive winter?
It survives winter as an adult, tucked into cracks, crevices, and wall voids for shelter, becoming active again once warm weather returns in spring, which is why large numbers sometimes emerge inside homes during a warm spell in late winter.