Boxelder Bugs and the Sunny Side of an Ohio House

Boxelder bugs gather on the south and west walls of Ohio houses in late September because those walls hold the most afternoon heat, and the bugs are hunting for somewhere protected to spend the winter. They do not bite, they do not breed indoors, and they do not damage the building. The fix that lasts is sealing the openings they are using.

Ohio State University Extension has already run its fall alert for this group, and the weather in Stark County is setting up the trigger it describes. Warm afternoons, then nights cool enough to send everything looking for cover. Extension explains that when a cold snap is followed by a warm spell, the adults use their wings to disperse in search of a place to overwinter. The wall they land on is the warm one.

Which Bug Is On Your Siding?

Three insects do most of this in Northeast Ohio, and Extension treats them as one problem with one answer. Its Buckeye Yard and Garden Line calls boxelder bugs the long-running poster child for insects that invade homes in the fall, and calls multicolored Asian lady beetles and brown marmorated stink bugs the more notorious members of the group. Both of those are non-native, and both have a deserved reputation for arriving in huge numbers.

The stink bug is the newest arrival of the three. Extension records it as first documented in Ohio in December 2007, in Franklin County, and since then in 62 of Ohio's 88 counties. The lady beetle has a longer local history: Extension dates its Ohio debut to October 1993, when residents started reporting thousands of beetles congregating on homes and buildings. Extension covers leaf-footed bugs in the same fact sheet as boxelder bugs, because they show up on the same walls for the same reason.

Why It Is Always The South And West Wall

Because that is where the heat is. Extension explains that home-invading insects are drawn to solar heat radiating off southern and western facing roofs and outside walls, and to the warmth leaking out from inside, and that the combination leads them into attics, exterior wall voids and the spaces around door jambs and window frames.

The same behavior shows up on trees before it shows up on houses. Extension notes that when a cold snap hits in early fall, boxelder bugs gathering on tree trunks collect on the west side of the trunk to get the most out of the warming sun. A brick or vinyl wall facing the same direction holds heat better than bark does, and it comes with cracks.

This is also why the problem repeats. Extension notes that on warm days in winter and early spring the bugs come out onto light-colored surfaces on the south and west sides of buildings, resting in the sun. The wall that is covered today in North Canton is very likely the wall that will be covered again on the first mild afternoon in February.

Where The Boxelder Bugs Are Actually Coming From

From a tree, and a specific kind of tree. Extension's fact sheet says boxelder bugs feed on seed-bearing boxelder trees, meaning the female ones, and on seed-bearing silver maples, and that they do not feed on male trees. If a property nearby has a big seed-heavy boxelder or silver maple, that is the engine behind the crowd on your siding, even if the tree is not yours.

That is worth knowing because it sets realistic expectations. Nothing you do to your house stops the tree from producing bugs. What you can control is whether they spend the winter inside your wall or somewhere else.

What They Do, And Do Not Do, Once They Are In

Less than most people fear. Extension states that these bugs do not cause damage to buildings, clothing, food or humans, and that the trouble is their presence: the foul odor when they are crushed or disturbed, and the staining they leave behind. Nobody is losing structural timber to a boxelder bug. The complaint is the crunch underfoot and the marks on the curtains.

They also cannot build a population indoors. Extension says only full-grown adults survive the winter, and that the overwintering adults leave their hibernation sites when warm weather arrives, around the last week of March in Ohio, with females starting to lay eggs in late April or early May. There is no indoor generation in between. A bug walking across the ceiling in January is a survivor from September trying to find its way back outside.

Heated rooms are a dead end for them. Extension notes that when these insects end up in warm indoor space rather than a cool void, the high temperature burns through their fat reserves and they eventually starve. Extension lists their preferred hiding spots as cracks and crevices in walls, door and window casings, around foundations, stone piles and tree holes. The ones you see in the living room are the fraction that guessed wrong.

The Sealing List, And The Order To Work It

Extension is blunt about the priority: Plan A is sealing the openings that let the invaders in. Everything after that is cleanup. Work it from the roof down while the weather still lets you get on a ladder.

• Attic and soffit vents. Extension tells homeowners to inspect the attic for unprotected vents, naming bathroom and kitchen vents and unscreened attic vents specifically. An unscreened gable vent is a wide open door in a lot of older houses.
• Window frames and door jambs. Extension points at caulk that has failed around window frames and door jambs as easy access, and recommends a good quality flexible caulk for the gaps, with an insulating foam sealant for the larger openings.
• Door sweeps, garage included. Worn-out exterior door sweeps get called out by name, and Extension includes the door from the house into an attached garage, which is the one almost everybody forgets.
• Siding and screens. Poorly attached siding and rips in window screens are both on Extension's list. A loose corner of J-channel leads straight into the wall void.
• Utility penetrations. The EPA recommends caulking small gaps, filling larger ones around pipes with steel wool, and covering holes with wire mesh. Dryer vents, hose bibs, gas lines and AC line sets all qualify.
• The odd ones. The EPA adds window-mounted air conditioners, exhaust fans, ceiling fixtures, baseboards and chimneys to the list of typical entry points, and says mechanical exclusion is the best method available for keeping stink bugs out.

Timing matters more here than technique. This work is worth far more this week than in November. Seal a wall after the bugs have already moved into the void and the caulk works against you: they are inside with nowhere to go, and the exit they eventually find may be on the room side of the drywall.

Why Spraying Is The Wrong First Move

Partly because it does not address the gap, and partly because of where the product ends up. The EPA is direct that many chemicals intended for outdoor use are dangerous indoors, since they stay toxic far longer inside than they would outside. It advises that products not contained in baits or traps be applied to targeted locations rather than sprayed across a whole room, and that fogging devices be used only when they are genuinely necessary.

For lady beetles, Extension goes further and says insecticide treatment is not suggested at all, on the grounds that lady beetles are beneficial and not harmful to humans. Its recommendation is to caulk and seal the gaps, then physically remove the beetles that are already indoors.

So vacuum, do not swat. Extension warns that the reflex bleeding from a disturbed lady beetle can leave permanent stains, and its boxelder bug fact sheet notes the foul odor these bugs give off when crushed. A vacuum with the bag or canister emptied outside avoids both problems.

When It Is Worth Handing It To Someone Else

A scatter of boxelder bugs on the siding in late September is an ordinary Ohio autumn. It is worth a call when the picture changes: the sunny wall is covered rather than dotted, you are finding them indoors every day, the house has older wood windows or an unfinished attic with open vents, which describes a lot of the housing stock around Canton and Akron, or you have watched the same thing happen three falls in a row.

Seasonal invaders are on the covered list for State Shield Essential, the quarterly plan, alongside ants, spiders, millipedes, centipedes, cockroaches, mice, rats, bees and wasps. Four visits a year means somebody is working the exterior in late summer and again in fall, before the bugs are in the wall rather than after. If pests come back between treatments, so do we, at no cost.

The gaps are worth closing for a second reason. The same soffit seam and the same worn door sweep that let boxelder bugs in this month let mice in a few weeks later, once the nights get genuinely cold. That is usually one trip around the building rather than two.

If your sunny wall is already covered and you would rather not spend a Saturday on a ladder, we will walk the outside of the house and tell you where they are getting in. Get a free estimate through our request form, or call 330-494-6199.