Stink bugs and Asian lady beetles: why they invade in fall and how to keep them out
Published Updated
By John Stopka, Co-Founder & CEO · Reviewed by John Stopka
Stink bugs and Asian lady beetles gather on homes in the fall and squeeze inside to spend the winter [1][2][3]. In Kentucky, stink bugs start moving in around early to mid September, and Asian lady beetle flights peak in October [1][2]. They don't breed or damage the house indoors, and sealing gaps before fall is the most lasting way to keep them out [1][2].
Why do stink bugs and Asian lady beetles come into houses in the fall?
To spend the winter. Shorter days and cooler temperatures trigger the urge to find a sheltered place to overwinter [1].
In nature, brown marmorated stink bugs look for cool, dry, protected spots like rock outcrops and dead trees with loose bark. A house offers the same kind of shelter [1]. Asian lady beetles fly to buildings looking for overwintering sites, too [2][3].
Once inside, lady beetles tuck into cracks around window and door frames, behind siding and fascia boards, and into soffits, attics and wall voids [2]. Stink bugs favor the upper parts of a building and often get in through attics and chimneys [1].
When do they come inside in Kentucky and Illinois?
Stink bugs come first. In Kentucky, brown marmorated stink bugs start entering buildings in early to mid September [1].
Asian lady beetles follow. In Kentucky, their flights to buildings peak in October, but they can run from September into November depending on the location and the weather [2]. Flights are heaviest on sunny afternoons after a cool spell, once temperatures climb back to at least the mid-60s [2]. Stink bug flights also peak on warm, sunny afternoons [1].
University of Illinois Extension describes the same fall pattern for both insects in Illinois [3].
How do you identify stink bugs and Asian lady beetles?
The stink bug is shield-shaped and mottled brown. The Asian lady beetle is about 1/4 inch long, with a dark M or W mark behind its head [1][2][3].
| Feature | Brown marmorated stink bug | Asian lady beetle |
|---|---|---|
| Shape and size | Shield-shaped, about 5/8 inch long | A lady beetle about 1/4 inch long |
| Color | Mottled or marbled brown | Tan, yellow or red-orange |
| Key marks | White bands on the antennae, and light and dark bands on the legs and the edge of the abdomen | A dark M- or W-shaped mark on the whitish area behind the head, and anywhere from none to 19 spots |
| When disturbed | Gives off a strong smell, often compared to cilantro | Gives off a sharp odor and a yellowish fluid |
Other bugs come inside in fall too. Boxelder bugs and western conifer seed bugs are sometimes mistaken for stink bugs [1].
What is a western conifer seed bug?
The long, brown bug that shows up in fall and buzzes loudly when it flies is usually a western conifer seed bug.
It is about three-quarters of an inch long, narrower than a stink bug, with a thin white zigzag across its back and flat, leaf-shaped flares on its back legs. That leg shape is the quickest way to tell it from a stink bug, which is broad and shield-shaped with plain legs.
Outdoors it feeds on the seeds and cones of pines and other conifers. In fall it does exactly what stink bugs and lady beetles do: it looks for somewhere sheltered to spend the winter, and a warm wall or attic will do.
It is harmless to people and the house. It does not bite or sting, it does not breed indoors, and it does not eat wood, fabric or food. Handled roughly, it gives off a sharp, piney smell. Keeping it out is the same job as keeping stink bugs out — sealing the gaps it comes through.
What are boxelder bugs?
Black bugs about half an inch long with thin red or orange lines on the back, and bright red underneath. Boxelder bugs feed on the seeds of boxelder trees and some maples, and in fall they gather by the hundreds on sunny south- and west-facing walls before looking for a gap to spend the winter in — the same pattern as stink bugs and lady beetles.
They are harmless: they do not bite people, do not breed indoors and do not damage the house, though their droppings can spot light-colored curtains and walls. Sealing the same gaps that keep out stink bugs keeps them out too.
Do stink bugs and lady beetles damage your home?
Not the house itself. Neither insect breeds indoors, and the ones you see in late winter or spring are the same insects that came in during the fall [1][2]. Asian lady beetles don't attack wood, food or clothing [2], and stink bugs cause no structural damage [1].
They're still a nuisance:
Do Asian lady beetles bite?
Yes — and it is one of the things that separates them from the ladybugs people remember fondly.
University of Kentucky: "When large numbers of beetles are flying in the fall, they often land on clothing and occasionally will bite or 'pinch' if in contact with skin" [2]. As for how it feels, "The bite feels like a pinprick and is seldom serious" [2]. They have chewing mouthparts because in nature they eat other insects [2].
Colour is the other question, usually asked right after being bitten by an orange one. UK describes their colour as varying "widely from tan to orange to red," often with "several black spots on the wing covers," though on some beetles the spots are faint or missing [2]. An orange one is not a different, angrier insect. It is the same beetle.
If a bite bothers you, that is a question for a healthcare provider.
Do stink bugs bite or sting?
No. Stink bugs have a narrow, straw-like beak built for piercing plants and sucking out the juice, not for biting people, and they have no stinger. They are not poisonous and not dangerous to people or pets. Their only defense is the smell.
Why do stink bugs stink?
It is how they protect themselves. When a stink bug is disturbed, handled or crushed, glands on the underside of its body release a strong-smelling chemical meant to put off birds and other predators. Most people compare it to cilantro, and it lingers.
That is why crushing them, or sucking them into a household vacuum, tends to leave the smell behind. The fluid can also leave a stain on light fabric and walls.
Can stink bugs fly?
Yes. Adult stink bugs have full wings under the shield-shaped back and fly well, with a loud, clumsy buzz. That flight is how they reach houses in the fall, landing on sunny, warm walls in the afternoon and then crawling into gaps. The young ones, called nymphs, have no wings and cannot fly.
What do stink bugs eat, and where did they come from?
Outdoors, the brown marmorated stink bug feeds on plant juices from a long list of crops and garden plants — apples, peaches and other fruit, tomatoes, peppers, sweet corn, beans and soybeans, and many ornamental trees and shrubs. The feeding leaves dimpled, discolored spots on fruit.
Inside your house, they do not eat anything. They are there to wait out the winter, not to feed or breed.
The brown marmorated stink bug is not native. It comes from East Asia and was first confirmed in the United States in Pennsylvania in the late 1990s, most likely carried in with shipping. It has since spread across most of the country, including Kentucky and Illinois. Native stink bugs, such as the green stink bug, live here too, but they rarely come indoors in numbers.
How long do stink bugs live?
Adults can live most of a year. The ones that come inside in September and October survive the winter in walls and attics, come out in spring, and lay eggs on plants outdoors. The next generation grows up over the summer, and the adults of that generation are the ones heading for your house the following fall.
How do you keep stink bugs and Asian lady beetles out?
Seal them out before they arrive. University of Kentucky entomologists call sealing entry points the most permanent way to keep fall invaders out, and the best time to do it is late spring or summer [1][2].
- Caulk cracks around windows, doors, soffits and fascia boards, and where pipes and wires enter the house [1][2].
- Put tight-fitting door sweeps or thresholds on exterior doors [2].
- Fix holes in window screens, and make sure windows and doors fit tightly [1][2][3].
- Add screening behind attic vents [1][2]. Use fine mesh: in UK testing, many adult stink bugs got through 1/4-inch screening [1].
- Remove or seal around window air conditioners in the fall [1].
- Keep siding, eaves and soffits in good repair, and seal gaps around the foundation and chimney [3].
How do you get them out of the house without chemicals?
Vacuum them up or move them out by hand.
- Vacuuming is the easiest way to remove lady beetles [2]. A vacuum may smell like stink bugs for a while afterward. A nylon stocking placed in the hose catches the bugs before they reach the bag [1].
- To pick up stink bugs by hand, use gloves or a tissue. You can also hold a container under a bug and nudge it to drop in [1].
- Illinois Extension suggests emptying vacuumed bugs into soapy water [3].
How does Liberty treat stink bugs and Asian lady beetles?
Here's what we do.
On your first visit, your Service Specialist does a thorough inspection inside and outside to see how many stink bugs there are, where they're getting in and what draws them, like sunny walls and gaps around windows, siding and attic vents.
- Treat windows and eaves: Outside, your Service Specialist treats around window and door frames and eaves, where stink bugs gather and look for a way in.
- Treat siding and vents: They also treat the sunny sides of your home, siding and attic vents, where stink bugs rest before moving inside.
- Inside treatment: Your first visit always includes treatment inside where stink bugs gather, like around windows, and on later visits they treat inside only if it's needed and ask you first.
For Asian lady beetles:
- Outside, your Service Specialist treats around window and door frames and eaves, where lady beetles cluster in the fall.
- They also treat the sunny sides of your home, siding and attic vents, where lady beetles gather in the fall.
If covered pests show up between visits, just text us.
In Western Kentucky and Southern Illinois, our stink bug and Asian lady beetle calls usually start in October.
When to call a professional
Call if large numbers keep getting inside after you've sealed what you can, or if the gaps are in places you can't reach, like soffits and roof lines.
Stink bugs and Asian lady beetles are covered by every Liberty pest control plan. Learn more on our pest control page, or read about stink bugs and Asian lady beetles in our pest library.
Common questions
When do stink bugs come inside in Kentucky?
Brown marmorated stink bugs start entering buildings in Kentucky in early to mid September, looking for a place to spend the winter [1].
When do Asian lady beetles invade homes?
In Kentucky, Asian lady beetle flights to buildings peak in October and can run from September into November. They're heaviest on sunny afternoons after a cool spell [2].
Do stink bugs lay eggs in your house?
No. Brown marmorated stink bugs don't breed or reproduce indoors. The stink bugs you see in winter and spring are the same ones that came in during the fall [1].
What's the best way to keep stink bugs out?
Seal cracks around windows, doors, soffits, fascia boards, pipes and wires, and fix screens, ideally in late spring or summer before the bugs arrive [1][2].
Do stink bugs bite?
No. Stink bugs have a beak for sucking plant juices, not for biting people, and they have no stinger. They are not poisonous or dangerous to people or pets.
Why do stink bugs smell?
When disturbed or crushed, they release a defensive chemical from glands on the underside of the body. The smell is often compared to cilantro and lingers, which is why crushing or vacuuming them leaves it behind.
Can stink bugs fly?
Yes. Adults fly well, with a loud buzz, and that is how they reach houses in the fall. Young stink bugs have no wings.
Where did stink bugs come from?
The brown marmorated stink bug is native to East Asia and was first confirmed in the United States in Pennsylvania in the late 1990s. It has since spread across most of the country, including Kentucky and Illinois.
Do ladybugs bite?
Asian lady beetles do. University of Kentucky says that when large numbers are flying in the fall they "often land on clothing and occasionally will bite or 'pinch' if in contact with skin" [2].
Do orange ladybugs bite?
Colour does not change the answer. Asian lady beetles vary "widely from tan to orange to red" [2] — an orange one is the same insect as a red one.
Does an Asian lady beetle bite hurt?
University of Kentucky describes it this way: "The bite feels like a pinprick and is seldom serious" [2]. If a bite bothers you, ask a healthcare provider.
What is the long brown bug that comes inside in the fall?
Usually a western conifer seed bug: about three-quarters of an inch long, with leaf-shaped flares on its back legs and a loud buzz in flight. It comes in to spend the winter, and it does not bite, sting, breed indoors or damage the house.
Are boxelder bugs harmful?
No. Boxelder bugs do not bite people, breed indoors or damage the house. They gather on sunny walls in fall and slip in to spend the winter, like stink bugs.
Why do Asian lady beetles gather on one side of the house?
They're drawn to the sunnier southwest sides of buildings that get afternoon sun, and to contrasting light and dark features like dark shutters on a light wall. Homes near woods tend to get more [2].
Sources
- University of Kentucky Entomology. "Stink Bug Infestation of Dwellings." https://entomology.mgcafe.uky.edu/ef654 (opens in a new tab)
- University of Kentucky Entomology. "ENTFACT-416: Asian Lady Beetle Infestation of Structures." https://entomology.mgcafe.uky.edu/ef416 (opens in a new tab)
- University of Illinois Extension. Ken Johnson, "Fall House Guests." October 1, 2019. https://extension.illinois.edu/blogs/good-growing/2019-10-01-fall-house-guests (opens in a new tab)