Boxelder bugs, multicolored Asian lady beetles and brown marmorated stink bugs gather on warm, sunny walls in Indianapolis during September and October, then squeeze through gaps to spend the winter inside walls and attics. They do not damage the house or feed on anything indoors, but they stain, smell and reappear on warm days until spring.
Key takeaways
- Boxelder bugs, Asian lady beetles and brown marmorated stink bugs look for winter shelter in September and October and often reappear indoors on warm winter days and in early spring.
- Boxelder bugs favor seed-bearing female boxelder trees, so a block with several of those trees can see heavy numbers on south- and west-facing walls.
- Asian lady beetles eat aphids outdoors and do not damage anything indoors, but they give off a foul-smelling fluid that can stain and may pinch bare skin.
- Purdue's Plant & Pest Diagnostic Laboratory confirmed Indiana's first brown marmorated stink bug in October 2010, from a homeowner's sample in Elkhart County.
- Vacuuming is the cleanest way to remove these bugs indoors; crushing them releases odor and stains.
- A fall overwintering-pest treatment with perimeter treatment and sealing is estimated at $175–$450 and is most effective before the bugs get into the walls.
Why do these bugs pile onto Indianapolis houses every fall?
All three are overwintering insects. As days shorten and nights cool in September and October, they leave trees, gardens and fields to find a protected spot for winter, and a sun-warmed house wall is the obvious choice. From there they slip under siding, around window frames and into attics and wall voids.
Indoors they go quiet in the cool parts of the house. On a warm afternoon, or when furnace heat reaches the wall they are hiding in, some wake up and crawl toward light. That is why they show up at windows in January and February and again as spring arrives.
East-side houses give them plenty of room. Clapboard siding on Victorians and Foursquares, wood storm windows, window air conditioners and attic vents on old Irvington and Woodruff Place homes all leave gaps, and the big shade trees that make those streets so pleasant also feed and shelter the bugs all summer.
Newer subdivisions are not immune. Homes in Cumberland, McCordsville and Fishers that face open fields or woods to the south and west take the full afternoon sun, and that is exactly the wall these insects look for. The Indianapolis pest calendar shows where this fits in the rest of the year.
How do you tell boxelder bugs, lady beetles and stink bugs apart?
Shape and color are the giveaways. Boxelder bugs are long, flat and dark with red lines on the back. Asian lady beetles are round, yellow-orange to red, often with black spots and an M-shaped mark behind the head. Brown marmorated stink bugs are shield-shaped and mottled brown, with light bands on the antennae.
Native lady beetles also show up in gardens, but the ones that collect by the hundreds on a house in late October are usually the Asian species. A strong musty smell when you brush them off a sill is a good clue.
Young boxelder bugs look different from adults: bright red and wingless. Seeing them on a tree trunk in summer is an early warning that fall will be busy on that side of the house.
| Feature | Boxelder bug | Asian lady beetle | Brown marmorated stink bug |
|---|---|---|---|
| Size and shape | About 1/2 inch, long and flat | About 1/4 inch, round and domed | About 5/8 inch, shield-shaped |
| Color | Dark brown to black with red markings; young are bright red | Yellow-orange to red, with or without black spots; black M behind the head | Mottled brown with light bands on the antennae |
| Where they gather | Sunny south and west walls, often near boxelder trees | Light-colored or sunny walls, especially near woods | Sunny walls, window frames, soffits and attic vents |
| Outdoor food | Seeds and sap of boxelder and some other trees | Aphids and other soft-bodied insects | Fruit, vegetables, ornamental plants and crops |
| Indoor nuisance | Spots from droppings; clusters at windows | Foul odor and staining fluid; may pinch bare skin | Strong odor when crushed or disturbed |
| Peak entry | September–October | Mid- to late October | September–October |
Why are boxelder bugs worse on some Indianapolis streets?
Boxelder bugs feed and lay eggs mainly on female, seed-bearing boxelder trees, so blocks with a few of those trees, or with other host trees nearby, see far more bugs. In fall the adults leave the trees for the sunniest walls close by, which on many east-side lots means the south and west sides of the house.
Boxelder is a fast-growing member of the maple family that tends to seed itself along creeks, alleys and fence lines, so it is easy to find near Pleasant Run and in overgrown corners of older lots. Many owners do not realize they have one until they notice clusters of winged seeds hanging on into winter.
Purdue Extension notes that eggs can also be laid on ash, maple, plum, cherry and other trees. Through summer the young feed in the canopy. By late fall the adults bunch up on warm siding, foundations, sidewalks and porch rails before working into cracks in the foundation, around windows and doors, and under siding and shingles.
Cutting down a female boxelder may lower numbers over time, but bugs also fly in from neighboring yards. Sealing the house and timing a perimeter treatment for early fall usually does more. See boxelder bug control for what that visit covers.
Are Asian lady beetles harmful?
Mostly they are a nuisance. Purdue Extension notes that Asian lady beetles indoors do not feed on or damage anything, infest food or harm furnishings. The trouble is their numbers, a foul-smelling fluid they release when disturbed that can stain walls and curtains, and an occasional pinch on bare skin.
Outdoors they are helpful, eating aphids and other soft-bodied insects on trees, crops and garden plants all summer. The problem only starts when they cluster on a house.
They gather in mid- to late October, often on light-colored houses or homes near woods, and Purdue notes a preference for southwest-facing walls. Houses near the wooded edges of Ellenberger Park, Fort Harrison State Park or the ravines of Meridian Hills can see heavy numbers.
Indoors, vacuum them rather than sweeping or swatting, which squeezes out the fluid. If they keep appearing in one room, the gap is usually nearby: a window frame, a ceiling light fixture or an attic hatch. Our Asian lady beetle control page explains how those spots are handled.
When did brown marmorated stink bugs reach Indiana?
Indiana's first confirmed brown marmorated stink bug came from a homeowner in Elkhart County in October 2010, identified by Purdue's Plant & Pest Diagnostic Laboratory. The insect is native to East Asia and was first reported in the U.S. in Pennsylvania in 1998. It has since spread widely in Indiana.
In Purdue Extension's description, adults come out in spring from late April to mid-May, feed through the summer on fruit, vegetables and ornamental plants, and are drawn to buildings from September through October. Backyard gardens and fruit trees keep them fed until then.
The name says it all. When crushed or threatened, the bug releases a pungent chemical, so swatting one on a curtain is a mistake. Knock it into a jar of soapy water, or vacuum it with a bag you can seal and throw out.
Stink bugs are also a crop and orchard pest, which matters to gardeners and small farms in Hancock County and Franklin Township, but indoors they are only a nuisance. A stink bug control visit focuses on keeping them out of the house.
How do you get them out of the house without making it worse?
Vacuum them up and empty or seal the bag right away, or knock them into a container of soapy water. Do not crush them, because all three release odors or stains. Avoid spraying insecticide into walls, since dead bugs left in a wall void can attract carpet beetles and other scavengers later.
A shop vacuum works, or a regular vacuum with a knee-high stocking pushed into the hose and held with a rubber band. The stocking catches the bugs before they reach the bag; tie it off and throw it out.
Sticky window traps and light traps catch a few stragglers but do not touch the main group in the walls. Purdue Extension notes that household sprays give only temporary relief indoors, so the real work happens on the outside of the house before the bugs go in.
If you are unsure which bug you have, save a few in a sealed bag or take a sharp photo. The technician, or the Purdue Plant & Pest Diagnostic Laboratory, can confirm the species, which helps because lady beetles tend to arrive a few weeks later than the other two.
When should a fall perimeter treatment and sealing happen?
Early to mid-September is the usual window in Indianapolis, before the first cold nights send the bugs into the walls. A technician treats the sunny walls, eaves, window and door frames and other places the bugs gather, following the product label, and seals the gaps they use. Once they are inside, treatment mostly helps with stragglers.
The estimate for a Fall overwintering-pest treatment (boxelder bugs, Asian lady beetles, stink bugs: perimeter treatment + sealing) is $175–$450 in 2026. Big Victorians with many windows, tall gables and clapboard siding land toward the top of that range; a brick ranch with vinyl windows sits near the bottom. The price is confirmed and approved before treatment.
Second-story gaps matter more than most people expect. Lady beetles and stink bugs fly, so they reach gable vents, dormer trim and the tops of window frames as easily as the foundation, and those high spots are where many tall Victorian houses leak the most.
In Irvington and other locally protected historic districts, check with the Indianapolis Historic Preservation Commission before changing visible exterior features such as vent covers or trim.
To set up a visit before the bugs move in, call (855) 974-4733.
- Gaps where window air conditioners sit in the frame
- Loose or cracked caulk around window and door trim
- Openings under siding laps and at corner boards
- Unscreened attic, soffit and gable vents
- Spots where cable, phone and gas lines enter
- Worn weatherstripping on attic doors and hatches
Frequently asked questions
Will these bugs damage my house or furniture?
No structural damage. Boxelder bugs can leave droppings that spot curtains and siding, lady beetles release a fluid that stains, and stink bugs smell when disturbed. None of them eat wood, fabric or stored food.
Do they lay eggs in my walls?
They are not breeding while they overwinter. The adults that move in during fall wait out the cold and head back outdoors in spring, where they mate and lay eggs on trees and plants. That is why sealing in late summer does more than treating inside.
Why are stink bugs crawling in my kitchen in March?
They spent the winter in your walls or attic and are trying to get back outside as the days warm up. Some end up in living space instead. Vacuum them, note which windows and rooms they appear in, and seal those areas before next September.
Should I cut down my boxelder tree?
It can reduce boxelder bugs over time if it is a female, seed-bearing tree, but neighbors' trees will still supply some. Most owners get more from sealing the south and west walls and timing a perimeter treatment for early fall. Talk to an arborist before removing a healthy tree.
Do bug zappers or indoor foggers help?
Not much. Foggers do not reach bugs tucked into wall voids, and dead insects left in the walls can draw carpet beetles. A vacuum handles the ones you can see, while exterior sealing and a well-timed perimeter treatment handle the rest.
Sources
- Purdue Extension Entomology – Boxelder Bugs (E-24)
- Purdue Extension Entomology – Asian Lady Beetle (E-214)
- Purdue Extension Entomology – Brown Marmorated Stink Bug in Homes (E-273)
- Purdue University News – Brown marmorated stink bug reported in Indiana for first time (2010)
This guide is general information for Marion County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.