Boxelder bugs are flat black insects about 1/2 inch long, with red or orange lines behind the head and along the wings and a bright red abdomen underneath. They feed on boxelder, maple and ash trees, and in fall they gather by the hundreds on sunny walls before squeezing into houses to spend the winter. They don’t bite, breed indoors or damage your home. The trouble is their numbers, the stains they leave and their smell when crushed.
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What Boxelder Bugs Look Like
- Size: about 1/2 inch long and somewhat flattened.
- Color: black to brownish-black, with three red or orange lines behind the head, a red line along each side and red edges on the wings.
- Underneath: the abdomen is bright red, which you see when the bug lifts its wings or flies.
- Nymphs: bright red and wingless, with black legs and antennae. Older nymphs show black wing pads.
- Eggs: tiny, straw-yellow at first and turning red, laid in small groups in bark cracks and on leaves.
Eastern vs western boxelder bug
The eastern boxelder bug (Boisea trivittata) lives across most of the eastern U.S. and Canada and west through the Great Plains, with populations in parts of the Rockies and California. The western boxelder bug (Boisea rubrolineata) ranges from British Columbia to California and east to Utah and Texas. They look almost the same; the western species has narrower, paler red bands and red wing veins.
Boxelder Bug Life Cycle
- Spring: adults leave their winter shelter from late March to early May, feed, mate and lay eggs on host trees.
- Eggs: hatch in about 10 to 19 days.
- Nymphs: molt five times as they grow, changing from all red to black with red markings.
- Summer: most areas have two generations a year; cooler areas may have one.
- Fall: adults gather on warm surfaces and move into shelter. Nymphs that haven’t matured die at the first frosts, so only adults survive the winter.
What Boxelder Bugs Eat
Boxelder bugs suck sap and juices from the seeds, new leaves, flowers and twigs of their host trees, and eat seeds that have fallen to the ground. Their main host is the boxelder tree, especially female trees that produce seeds; they are seldom found on male trees. They also feed on silver maple and other maples and on ash, and sometimes on ripe fruit such as apples, plums and peaches.
Feeding causes only minor damage: a little leaf yellowing, spotting or distortion, and occasionally pitted spots on fruit.
Why Boxelder Bugs Come Into Houses
As days cool in late summer and fall, boxelder bugs fly in, sometimes from up to 2 miles away, and cluster on the warm south and west sides of buildings, trees and rocks. From there they crawl into wall voids, attics, window and door frames, and gaps under siding to spend the winter.
On warm winter days, sunshine or furnace heat wakes some of them, and they wander into living rooms, sunny windows and light fixtures. They don’t breed or feed indoors. They leave their hiding places in late March or April to return to the trees.
Do Boxelder Bugs Bite?
Boxelder bugs are not known to bite in normal contact, and they have no venom or sting. Some extension services note one may pierce the skin if it is pressed against bare skin, causing a small red spot that fades without any lasting effect. They are not known to carry any disease.
Are Boxelder Bugs Harmful?
- People and pets: not reported to harm people, pets or livestock.
- Your house: they don’t chew wood, fabric or food.
- Stains: their droppings leave reddish-orange spots on curtains, walls, furniture and siding.
- Smell: they give off an unpleasant odor when crushed or disturbed, so don’t squash them indoors.
- Dead bugs: bugs that die inside walls can attract carpet beetles.
Boxelder Bug Look-Alikes
| Insect | How to tell it apart |
|---|---|
| Red-shouldered bug | Dark gray with only two red lines behind the head and no red lines on the wings. Feeds on goldenrain tree and chinaberry seeds, mostly in the South, and also invades homes. |
| Large milkweed bug | Mostly orange-red with broad black bands and patches. Boxelder bugs are mostly black with thin red lines. |
| Small milkweed bug | Black and red with a red X-shaped pattern and white spots on the wing tips. Found on milkweed. |
| Firebug | Short red wings with two large black spots each. Introduced in a few areas of the U.S. |
| Kissing bug | Long, cone-shaped head and a flat abdomen with red or orange marks around the edge. Feeds on blood, unlike boxelder bugs. |
| Stink bug | Wider, shield-shaped and brown or green, with no red lines. See stink bug pictures. |
How to Keep Boxelder Bugs Out
- Seal before late summer: caulk gaps around windows, doors, siding, utility pipes and vents, and fit door sweeps.
- Check screens: repair holes and use 16-mesh or finer screen on vents.
- Clear the foundation: keep a strip of 6 to 10 feet next to the south and west walls free of debris and dense plants.
- Soapy water outdoors: spray clusters on outside walls with about 5 tablespoons of dish soap per gallon of water. It only kills bugs it hits.
- Vacuum indoors: vacuum bugs inside and empty or seal the bag right away.
Insecticides help little. Outdoor sprays break down within days to a week in sunlight, many work poorly in cool weather, and sprays inside wall voids leave dead bugs that feed carpet beetles. Cutting down female boxelder trees reduces the bugs but doesn’t stop them, since they fly in from nearby. For the full step-by-step plan, see how to get rid of boxelder bugs permanently.
Boxelder bug control supplies
- Exterior caulk for gaps around windows and siding
- Door sweeps to close gaps under doors
- Handheld vacuum for bugs indoors
- Pump sprayer for soapy water on outside walls
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Another fall invader, the western conifer seed bug, is often mistaken for a stink bug or boxelder bug.
Boxelder bugs often share sunny walls with Asian lady beetles and cluster flies in fall.
FAQs
Adults are about 1/2 inch long, flat and black, with three red or orange lines behind the head and red lines along the edges of the wings. The abdomen under the wings is bright red. Young boxelder bugs are bright red and wingless.
Very rarely. Most extension services say they are not known to bite, and at most one may pierce the skin when pressed against it, with no lasting effect. They have no venom, can’t sting and don’t spread disease.
No. They don’t damage wood, fabric or food and aren’t reported to harm people or pets. The problems are their numbers, the stains their droppings leave on walls and curtains, and a bad smell when crushed.
In fall they look for a warm, protected place to spend the winter. They cluster on sunny south- and west-facing walls, then crawl into gaps around windows, siding and attics.
No. They don’t feed or lay eggs indoors. The ones you see inside in winter and spring came in the previous fall and are trying to get back outdoors.
Seed-bearing female boxelder trees, plus silver maples and ash, where they feed and breed. In fall, warm sunlit walls and gaps leading into the house draw them in.
Sources
- Penn State Extension: Boxelder Bug
- University of Missouri Extension: Boxelder Bugs
- Colorado State University: Boxelder Bug
- University of Kentucky Entomology: Boxelder Bugs
- Iowa State University Extension: Boxelder Bug
- USDA Forest Service: Boxelder Bugs (FIDL 95)
Facts in this guide are checked against the sources above and reviewed when they change. See how we research in our editorial policy.
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