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Identify Your Pest Crawling insects Boxelder bug

Crawling insects

Boxelder bug

Boisea trivittata · Also called: Box elder bug, eastern boxelder bug

The boxelder bug is a black and red insect that feeds mainly on the seeds of Manitoba maple trees. It is noticed in late summer and fall, when large groups gather on sunny walls and slip indoors to spend the winter.

Black boxelder bug adults with red markings clustered with bright red nymphs on a sunny wall
Quick facts

Size About 12 to 14 mm long

Colour Mostly black, trimmed in red; young ones are mostly red

Key feature Three red stripes behind the head and thin red edges on the wings

Season Late August to October outside; warm winter and spring days indoors

Where Sunny south and west walls, window frames, attics and wall voids

How to identify it

What it looks like

Adult boxelder bugs are flat, narrow and mostly black. Look for thin red trim along the wing edges and three red or orange lines on the section just behind the head. When the wings open, a bright red abdomen shows underneath.

Nymphs, the young stage, have no working wings yet. They are mostly bright red, which makes them easy to spot on tree trunks. Adults and nymphs are often seen together on Manitoba maple trees in summer. In fall they gather in large groups on warm, sunny walls.

Often confused with

Western conifer seed bug

Larger and brown rather than black and red, with flat, leaf-like widenings on the back legs. It also comes indoors in fall, often from nearby pine or spruce trees.

Clover mite

Clover mites are red specks under 1 mm long, with eight legs and very long front legs. Boxelder bugs have six legs, and the nymphs seen on walls in late summer are several millimetres long.
Know the signs

Signs to look for

Clusters on sunny walls

Dozens of black and red bugs sunning on the warmest side of the house, a fence or a window frame as the nights turn cool.

Bugs indoors on warm days

Slow-moving bugs on windows and sills in winter or early spring, after waking up inside the walls.

Small orange stains

Reddish orange spots on curtains, blinds, walls or light fabrics where the bugs have rested.

Nymphs on maple trees

Bright red young bugs feeding on Manitoba maple seeds and leaves, or crawling on the trunk, in summer.
Why it matters

Risks and damage

Boxelder bugs are a nuisance, not a danger. They do not sting or spread disease, and they rarely if ever bite people. They do not breed indoors or chew wood, food or fabric. Their droppings can leave small reddish orange spots on curtains, walls and light fabrics, and crushed bugs give off an unpleasant smell. Feeding damage to trees is minor.

In Alberta

Boxelder bugs are common in Alberta wherever Manitoba maples grow, including many neighbourhoods in Calgary and Edmonton. They gather on sunny walls from late August to October. Warm spells in winter and spring can bring hidden bugs out into rooms.

Did you know?

Boxelder bugs feed mostly on the seeds of female Manitoba maples. Male trees do not make seeds, so homes near seed-bearing trees tend to see the most bugs.

Prevention

How to keep them out

Seal gaps before late August

Caulk cracks around windows, doors, siding, vents and utility lines, and repair torn screens before the bugs look for winter shelter.

Add door sweeps

Fit tight door sweeps and weather stripping, especially on the sunny south and west sides of the home.

Vacuum, do not crush

Vacuum bugs found indoors and empty the bag or canister outside. Crushing them can cause stains and a bad smell.

Clean up seeds and debris

Rake fallen maple seeds and leaves, and clear debris piles near the house where bugs feed and shelter.

Choose trees with care

When planting, pick a seedless male Manitoba maple or another tree. Seed-bearing female trees support the most bugs.
When to call

When it is time to bring in a professional

Consider professional help if boxelder bugs return in large numbers every fall, if many are getting into attics or wall voids, or if they keep appearing in rooms all winter. High or hard-to-reach gaps are easier to seal with help. Technica’s licensed technicians can inspect your home and suggest the right approach.

Common questions

Frequently asked questions

Do boxelder bugs bite or damage my home?

They rarely if ever bite people, and they do not damage wood, insulation or food. The main problems are small stains from their droppings and the smell of crushed bugs.

Will boxelder bugs lay eggs in my house?

No. They do not breed indoors. They hide in walls and attics to survive the winter, then try to get back outside in spring to feed and lay eggs on host trees.

Why do they show up inside in the middle of winter?

Bugs sheltering in walls and attics can become active when sun or indoor heat warms their hiding spot. They then wander toward light and windows. They cannot breed indoors and slowly die off.

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