Boxelder bugs, multicolored Asian lady beetles and brown marmorated stink bugs are the fall invaders that can enter Iowa homes. Iowa State University Extension treats them as accidental invaders and says exclusion is the preferred control, with barrier sprays on the south and west sides applied before entry, around September to mid-October.
Key takeaways
- Boxelder bugs are black and red and about half an inch long, tied to boxelder and maple trees.
- Multicolored Asian lady beetles have a black W-shaped mark behind the head.
- Brown marmorated stink bugs can show up indoors in fall, according to an ISU entomologist.
- Exclusion is the preferred control, with tight windows, doors, screens and sealed gaps.
- Barrier sprays for the south and west sides must go on before the insects enter, around September to mid-October.
- Vacuuming what gets inside is part of the work, and the vacuum contents should be sealed and removed.
Which insects are the fall invaders in Iowa?
Iowa State University names boxelder bugs and multicolored Asian lady beetles as the fall invaders that overwinter indoors. Brown marmorated stink bugs were discussed by an ISU entomologist as a fall invader that can also show up indoors.
Boxelder bugs are black and red and about half an inch long. They feed on boxelder and maple trees during the warm months, and in the fall they move toward buildings. Their numbers vary a great deal from year to year, so one season may bring many and the next few.
Multicolored Asian lady beetles have a black W-shaped mark behind the head. They are predators in the garden during the summer, and in the autumn they gather on sunny walls and wander into buildings through small gaps. Brown marmorated stink bugs were mentioned in an October radio segment by an ISU entomologist, as an insect that can also show up indoors in the fall.
Why do these insects gather on sunny walls?
They are looking for a sheltered place to pass the cold months, and a warm, sunny wall gives them heat during the day and an edge to crawl along. The gap at a window or a siding seam gives them a way in.
The insects collect on the south and west walls because those surfaces get the most sun. A warm wall is attractive, and the insects that land there are often the ones that go on to find an opening.
Accidental invader is the term Iowa State University uses for these insects. They do not breed indoors and they do not eat the house, but a crowd of them can be a nuisance and can stain surfaces when disturbed.
Why is exclusion the first step?
Iowa State University recommends exclusion as the preferred control. Closing the openings keeps the insects from entering, and a barrier spray on the outside works only when the openings are controlled.
Exclusion means tight windows and doors, intact screens, and sealed gaps around the foundation, pipes, wires and chimneys. ISU also lists a band of gravel at the foundation, two to four feet wide, as part of the exclusion approach. Each opening is a route, and a spray applied to a house with open routes will be followed by the next arrivals.
Screens and seals are checked each year, because the work wears out. A gap that was sealed once may open again after the building settles.
When should barrier sprays be applied?
Barrier sprays on the south and west sides must go on before the insects enter. Iowa State University puts that window from September to mid-October. A spray applied after the insects are inside does not reach the wall voids where they overwinter.
The timing is set by the season and the movement of the insects, not by a single calendar date. A technician looks at the house and the season before setting the date for the barrier work.
The barrier is applied to the walls and the perimeter, with the surfaces the insects use. A homeowner should not apply a barrier product on their own without understanding the timing and the label.
What should I do with insects already indoors?
Vacuum them up rather than crushing them, seal the bag or empty the canister outside, and clean the surface. Crushing the insects releases a smell and can leave a mark on the wall or window.
A vacuum removes the bulk of the insects inside, and the bag or canister should be emptied outside and sealed. Wipe the window sill and the frame afterwards, and check the room for openings that let the insects in.
A technician will remove indoor insects during a visit and check the wall voids and ceiling lines where they tend to gather.
What is the calendar for fall invader work?
The table below sets out the steps Iowa State University's sourced material supports, from late summer through winter. Timing is set on the visit, not by the table alone.
The calendar gives a sense of the order of work. Exclusion is the first step and should come before the barrier window. The barrier is timed for September to mid-October. Indoor removal is handled as insects appear, and the openings are checked again after the first season.
The table uses only the steps and months that Iowa State University's sourced material gives. It does not give temperatures or freeze dates, which are not sourced for this area.
| Season | What to do | Why |
|---|---|---|
| September to mid-October | Barrier sprays on the south and west sides, applied before entry | ISU places this window before the insects enter |
| Late summer | Seal gaps, repair screens and check door sweeps | Exclusion is the preferred control |
| October | Watch sunny walls and window frames for gathering insects | Accidental invader season |
| Autumn | Seal openings against deer mice and white-footed mice | These mice move indoors in autumn |
| Year-round | Check for house mice inside the home | House mice live in homes all year |
Can a homeowner handle fall invaders alone?
A homeowner can seal small gaps, repair screens and vacuum insects inside. Gaps high on the walls, the eaves and the attic are harder to reach safely, and the barrier timing is easier to judge with a technician.
Start with the openings you can reach at ground level and around the windows. Check the door sweeps and the weatherstripping, and replace any that no longer meet the surface. Note the openings you cannot reach, and ask a technician to check them.
Calls to Des Moines Pest Control are answered 24/7 in Des Moines, and a same-day visit is offered when a technician is free.
How can a homeowner spot the entry points before a visit?
Walk the outside of the house in late summer and look for gaps at window and door frames, a worn screen, a door sweep that no longer meets the threshold, and openings where pipes, wires or vents enter the wall.
Look carefully at the south and west walls, where insects gather in the afternoon. Note any gap at a siding seam or a trim joint, and any screen with a hole. Mark the places on a photo or a sketch, so the technician can find them quickly.
Inside, look at the windows and the window sills, the ceiling lines and the light fixtures in rooms that get sun. Insects that have already entered often rest in those places.
Why is the timing of the barrier so important?
The barrier has to be on the surface before the insects move in. A spray applied too early may wear off, and one applied after the insects are inside does not reach the wall voids where they spend the winter.
Iowa State University puts the window at September to mid-October. A technician will judge the timing for the house on the visit, taking account of the season and the insects already seen. Calling in late summer gives the team the best chance to plan the barrier for the right week.
A barrier is applied with the label in mind and the surfaces the insects use. It is not a substitute for sealing, and it should not be relied on alone.
Do fall invaders harm the plants and the yard?
Boxelder bugs feed on boxelder and maple trees, and the trees along the lot are often their source. Iowa State University's guidance is about keeping the insects out of the house, and the yard advice focuses on the trees and the building edge.
A tree that hosts the insects can be a source of the invaders that reach the house, so the trees near the building are worth checking. The technician can point out the trees that touch the building, and suggest trimming branches that bridge the wall.
Trimming and sealing work together. The aim is to reduce the bridges from the trees to the house and to close the openings the insects use.
Can a fall invader problem return every year?
It can, if the openings that let the insects in are not closed. Iowa State University describes the numbers as variable from year to year, so a house can be quiet in one autumn and busy in the next.
The insects come back to the same kinds of spot, so a house with open gaps will be reached again. A sealed house is much less likely to see a steady arrival, although the insects can still find a new route.
A yearly check of the screens, the seals and the trees near the building is the simplest way to keep the house closed.
Frequently asked questions
Are boxelder bugs harmful to the house?
Iowa State University describes them as accidental invaders that do not breed indoors and do not eat the house. Their main effect is nuisance, and they can stain surfaces when disturbed.
Why do lady beetles come in around the windows?
They are looking for shelter and gather on sunny walls and window frames. A gap at the frame or the screen is the usual way in, which is why exclusion focuses there.
When is the barrier window?
Iowa State University gives September to mid-October as the time for barrier sprays on the south and west sides, before the insects enter. A technician sets the date for the house.
Do I need to spray the whole house?
Barrier work is applied to the sunny walls and the perimeter where the insects gather and enter. The technician will say which surfaces need treatment and which only need sealing.
Will my pets be affected by fall treatments?
Keep pets off treated surfaces until they have dried or settled, as the technician explains. Do not wipe the surfaces before the product has set, and follow the written instructions.
What should I do about stink bugs inside the house?
Vacuum them and seal the bag outside. Close the openings they used. A technician can check the house and the outside to find the route and advise on the barrier timing.
Sources
- Iowa State University Extension, Crops: fall nuisance invaders
- Iowa State University Extension, Yard & Garden
This guide is general information for Polk County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.