Boxelder bugs and brown marmorated stink bugs are the fall invaders that Purdue University Extension material names for Indiana. Boxelder bugs do not bite or sting, but they become a nuisance once they get indoors. They come in through gaps in the foundation, around windows and doors, and under siding and shingles, so sealing has to come first.
Key takeaways
- Purdue University Extension publication E-24 says boxelder bugs do not bite or sting but become a nuisance once they are indoors.
- Adult boxelder bugs look for protected cracks and crevices to overwinter in, and they get in through gaps in the foundation, windows, doors and siding.
- Boxelder bugs become active again on warm, sunny days in late winter or early spring and leave their shelter to look for egg-laying sites.
- A Purdue Extension county article calls the brown marmorated stink bug the bigger fall-invader problem in Indiana.
- Purdue's suggested control for bugs already indoors is a fly swatter and a vacuum cleaner or a broom and dust pan.
- Repairs made before the entry season are the step most likely to limit how many insects get inside at all.
What are boxelder bugs, and are they harmful?
Boxelder bugs are a nuisance rather than a threat. Purdue University Extension publication E-24 says they do not bite or sting, and they become a problem mainly because of their numbers indoors. They are a seasonal pest with a clear pattern, not an emergency.
Boxelder bugs are easy to tell apart by their size and color pattern, and they are most often noticed when they gather in numbers on the outside of a house. They do not bite or sting, and they are not a structural pest, so the reason to act is the nuisance of having them inside. The problem is the number of insects, not any harm to people or to the building.
That makes them a different case from carpenter ants or termites, where the question is whether wood is being damaged. Boxelder bugs are a seasonal visitor. They arrive in autumn, overwinter in the building and become visible again in late winter and early spring. Understanding that rhythm is the reason sealing matters: the easiest time to keep them out is before the first cold weather sends them looking for shelter.
Why do they come indoors at all?
Boxelder bugs come indoors to overwinter. Adults look for protected cracks and crevices, and a warm wall or attic offers the shelter they need through the cold. Once they find a route in, they tend to use it again.
Adult boxelder bugs spend the cold months in sheltered spaces, and Purdue University Extension notes that they look for protected cracks and crevices to overwinter in. A wall void, an attic, the gap behind trim or the space under siding can all do the job. Where the building is heated, the insects are sheltered from the worst of the cold, which is why the nuisance shows up indoors and not out in the field.
The shelter they choose is the same kind of gap that other pests use, so a sealing visit tends to help with more than one problem. A technician can look at the spots where insects are most likely to gather and at the openings that lead to them. Finding those openings early is more useful than cleaning up after the insects have settled in.
Where do they get in?
Boxelder bugs get in through small openings in the building envelope. Purdue University Extension names cracks in the foundation, gaps around windows and doors, and openings under siding and shingles. Each of these is a place to check before the entry season, not after the insects are inside.
The foundation is the first place to look, especially where siding meets the masonry or where a utility line runs through the wall. Cracks in the foundation can be small enough to miss, and they are a common way in for insects that want to get out of the weather. Windows and doors come next. A worn weatherstrip, a gap at the threshold or a screen that does not fit can each give an insect the opening it needs.
Siding and shingles are the third route. Gaps under the bottom edge of siding, around trim and at the roof edges can let insects into the wall void. A Purdue Extension county article notes that boxelder bugs cluster on the sides of houses before they get in, which means the outside of the house is where the work is most visible. Walking the building with a flashlight in late summer is a practical way to find these routes before the insects do.
Why do they wake up on warm days in winter?
Boxelder bugs do not stay inactive through the whole winter. On warm, sunny days in late winter or early spring, they become active again and leave their shelter. The movement is a sign that they are looking for a way out and for sites to lay eggs.
A warm, sunny afternoon in February can bring boxelder bugs out of a wall or attic and into a room, sometimes in numbers that surprise the people who live there. That is when the insects are most visible indoors. The warmth wakes them, and they move toward light, which usually means a window. Seeing one on a sunny windowsill in late winter is a common first sign that the season is turning.
The sign to notice is the movement in a warm room, not the size of the group. Purdue describes the leaving of winter shelter as the step where the insects look for egg-laying sites, so the activity is part of their normal cycle. A clean sweep in March is useful even if the house seemed quiet in January. The practical answer is to remove the insects by hand as they appear and to seal the entry points before the next autumn.
What about the brown marmorated stink bug?
A Purdue Extension county article calls the brown marmorated stink bug the bigger fall-invader problem in Indiana. It is worth knowing about because it also moves into buildings in autumn to look for sheltered spaces. Gap sealing is the common first step against both insects.
The brown marmorated stink bug is the fall invader that the Purdue Extension county article describes as the bigger problem in Indiana. It moves into buildings in the autumn in a general way similar to the boxelder bug, looking for sheltered spaces for the winter. Because the same kinds of gaps are used, the work to close them is not specific to one insect.
A sealing visit that covers the foundation, windows, doors and siding helps with the fall invaders as a group, not only one species. Purdue's comparison is a reason to look at the whole building rather than only the spot where a single insect was seen. A technician can talk through which insects have been seen on the property and what the entry points look like.
What do I do about the ones already inside?
Purdue University Extension's suggested control for bugs already indoors is simple: a fly swatter, and a vacuum cleaner or a broom and dust pan. Those tools deal with the insects already in the room. They do not stop the next ones from coming in through the same gap.
Start with what is visible. Insects on a window can be swatted, or gathered with a broom and dust pan, which keeps them out of the room. A vacuum cleaner works on insects in a corner, along a baseboard or in a window track. Empty the vacuum or its canister promptly afterward, so the insects do not come back out. These tools deal with the insects already in the building, which is the right answer for a small number.
Handling the insects by hand is the simple part. The harder question is what brings them in, and that is the gap that has to be found. It is common to focus on the inside of the house when the entry is on the outside, along the foundation, the siding or the window frame. Once the entry points are sealed, the number of insects arriving should decline, and the job becomes a short one each autumn.
Why do repairs have to come before the entry season?
Repairs made before the autumn move matter most. The fall-invader entry period starts in late summer, and peak entry into attics and wall voids comes around October. Once insects are inside a wall, sealing becomes harder and the nuisance is already in place.
The fall-invader window opens in late summer, and by October the peak of entry into attics and wall voids is under way. A repair made in August is easy to schedule and keeps the insects out of the building. The same repair made in October may come after insects are already in the wall, and the sealing then needs access to the void. Timing is therefore the main decision, not the material.
The practical plan is simple. In late summer, walk the building and note the cracks, gaps, worn weatherstrip and loose siding. Fix the foundation cracks, close the openings around windows and doors, and check the bottom edge of the siding and the trim. A technician can handle the work that needs a ladder or access to a wall void, and can say which repairs are needed before the entry season.
Frequently asked questions
Do boxelder bugs bite or sting?
No. Purdue University Extension publication E-24 says they do not bite or sting. They become a nuisance once indoors, mostly because of how many gather. Identifying them does not involve any bite or sting risk.
Will boxelder bugs damage the house?
Boxelder bugs are not a structural pest, and the reason to act is the nuisance indoors. They do not damage wood the way carpenter ants or termites can. A technician can confirm the insect and the pattern on site, and the sealing work is useful either way.
When do they show up inside?
Most are seen in the autumn, when they enter buildings to overwinter. They can be seen again on warm, sunny days in late winter or early spring, when they leave their shelter. The timing of that movement follows the weather, so a warm February is more likely to bring them out than a cold one.
Is the brown marmorated stink bug worse than the boxelder bug?
A Purdue Extension county article calls the brown marmorated stink bug the bigger fall-invader problem in Indiana. That is Purdue's comparison of the two as fall invaders. Both insects get in through the same kinds of gaps, so sealing helps with both. A technician can say which insects have been seen.
Can I use a spray for them?
No product is named on this page, and it does not recommend a specific one. Purdue's suggested control for insects already indoors is a fly swatter, a vacuum or a broom and dust pan. Sealing the gaps is the step that cuts down the numbers coming in. A technician can explain the options for a specific building.
When should I call a technician?
Call when you have found entry points you cannot reach, or when insects are arriving in numbers that cleanup cannot keep up with. Phones are answered 24/7, and a visit the same day is possible when a technician is free. Calling before the autumn entry season usually leaves more room in the schedule. Call (855) 974-4733 to book.
Sources
This guide is general information for Blackford County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.