Stink bugs, lady beetles and boxelder bugs in the house every fall

Updated November 10, 2026 · KeystoneProGuide editorial team

Which insects move into Pennsylvania homes in the fall?

This guide covers the three that the EPA and Penn State Extension describe. Each looks for a sheltered place to spend the winter.

• Brown marmorated stink bug. An invasive insect from Asia, introduced in the mid-1990s. The EPA says the highest concentrations in the country are in the mid-Atlantic region. It is shield-shaped, mottled brown and about the size of a dime.
• Multicolored Asian lady beetle. Also non-native. Penn State Extension says it was first seen in Pennsylvania in the fall of 1993 and quickly spread across the state. It eats aphids in gardens but is a fall-invading pest of homes.
• Boxelder bug. Brownish-black with reddish-orange stripes, found throughout the eastern United States, and a nuisance mainly around homes near boxelder trees, according to Penn State.

When do they arrive?

On warm, sunny days in early autumn. The EPA says stink bugs look for wintering sites in early autumn and gather on the outsides of buildings and near doors and windows. Penn State says lady beetles begin around the beginning of October, gathering on sunny afternoons after cold nights on the south and southwest-facing walls, and that boxelder bugs collect in large numbers on the sunny south side of trees and buildings as fall approaches.

In heavy years the numbers are large. The EPA says stink bugs can enter by the hundreds or thousands, Penn State that thousands of boxelder bugs may get into living areas, and that tens of thousands of lady beetles can gather in attics and walls. On warm winter days, Penn State says, lady beetles move out of the walls into rooms as warmth comes through.

Are they harmful?

Mostly they are a nuisance, though each has a drawback.

• Stink bugs do not bite people or pets, do not damage buildings, do not reproduce indoors and are not known to transmit disease, the EPA says. They release an unpleasant smell when disturbed or crushed, and some people may be sensitive to their allergens.
• Lady beetles occasionally bite. Penn State says infestations have been linked to rhinoconjunctivitis, asthma and facial swelling in some people, that their yellow defensive fluid smells and can spot walls, and that pets that eat them may get chemical burns in the mouth.
• Boxelder bugs cause no direct damage to the structure, contents or occupants, Penn State says.

None of the three breeds inside the house. Penn State says overwintering insects like these do not reproduce in buildings, and the EPA says the same of stink bugs.

What keeps them out?

Sealing, done before they arrive. Penn State calls mechanical exclusion the best method for both lady beetles and boxelder bugs:

• seal cracks around windows, doors, siding and utility pipes, behind chimneys and under the fascia with good quality silicone or silicone-latex caulk;
• repair or replace damaged window and door screens;
• cover attic vents, chimneys and exhaust vents with number 20 or finer screen mesh.

The EPA's stink bug list adds weather stripping and door sweeps, raking debris away from the foundation, sealing foundation cracks, securing crawlspace entries, and filling gaps around pipes with caulk or steel wool.

Why doesn't spraying indoors work?

Because the insects keep coming out of the walls. The EPA says aerosols and foggers kill stink bugs in living areas but will not prevent more from emerging from cracks once they dry, and are not a long-term solution. Penn State says the same of foggers for lady beetles and boxelder bugs, and adds that sprays aimed into cracks will not stop them emerging and are not a recommended treatment.

Treating the wall voids can make things worse. Penn State says insecticide in voids may kill thousands of insects, but carpet beetles may then feed on the dead ones and go on to attack woolens and stored goods.

The EPA also warns that total release foggers use flammable propellants that can cause a fire or explosion when misused.

What should you do with the ones inside?

Vacuum them. Penn State says vacuuming is the most efficient way to remove lady beetles, and the EPA and Penn State both suggest it for stink bugs and boxelder bugs; the EPA notes the vacuum may smell of stink bugs for a while. To find where they are getting in, Penn State says to look for cracks under or behind baseboards, around window and door trim, and around ceiling exhaust fans and lights, and to seal them. It notes lady beetles are drawn to light coming through cracks, so start with the rooms where most appear.

When does a professional treatment help?

On the outside, at the right moment. Where sealing the whole exterior is difficult or impossible, Penn State says an exterior insecticide treatment by a licensed pest control operator may offer some relief, applied in fall just before the insects gather; for lady beetles it gives the window as late September or early October. It warns that sunlight breaks the product down, so the effect may last only several days to a week or two. The EPA similarly says a professional can treat vegetation by the foundation with products registered for outdoor residential use.

A company applying insecticide around the outside of your house is making what Pennsylvania's regulation calls a perimeter treatment, defined as pesticide applied to the exterior of a structure, up to 10 feet from it unless the label says otherwise. It needs a state pesticide business license and a certified applicator; Penn State suggests asking for the card and checking the BU number on the vehicle.

Ask any company offering a fall treatment whether it will also seal entry points, which is what Penn State and the EPA put first. For the calendar of other pests, see how often and when, and for what to ask before hiring, see questions to ask.

Sources

1. Brown Marmorated Stink Bug, U.S. Environmental Protection Agency
2. Multicolored Asian Lady Beetle, Penn State Extension
3. Boxelder Bug, Penn State Extension
4. Safety Precautions for Total Release Foggers, U.S. Environmental Protection Agency
5. 7 Pa. Code Chapter 128. Pesticides, Commonwealth of Pennsylvania (Pennsylvania Code)
6. Choosing a Qualified Pest Management or Lawn Care Company, Penn State Extension