Common House Bugs in Pennsylvania, Season by Season
The most common house bugs in Pennsylvania are fall invaders that overwinter in walls and attics (brown marmorated stink bugs, multicolored Asian lady beetles, boxelder bugs, cluster flies and western conifer seed bugs), plus black carpenter ants, odorous house ants, house centipedes, camel crickets and eastern subterranean termites. Spotted lanternflies are active outdoors from July until hard freezes, and Pennsylvania reported the second most Lyme disease cases of any state in CDC’s 2023 data. Most of these pests are nuisances that sealing in late summer prevents. Termites and carpenter ant nests in wet wood are the jobs for a licensed professional.
Pennsylvania’s house bug calendar is driven by its winters. Many of the insects people find indoors are not breeding there at all: they move in during autumn to survive the cold, then wander into living areas on warm days. Two of the state’s best-known invaders, the brown marmorated stink bug and the spotted lanternfly, were first found in North America in eastern Pennsylvania. This guide goes season by season, using Penn State Extension fact sheets, and adds our own count of what Pennsylvanians photograph.
Pennsylvania house bugs, season by season
| Season | What you will usually see | What it means |
|---|---|---|
| Late winter to early spring | Black winged termites swarming at basement windows and doors | An active termite colony in the building; call a professional |
| Winter warm spells | Stink bugs, lady beetles and cluster flies at windows; house centipedes at night | Overwintering insects leaving wall voids; vacuum and seal |
| Spring to early summer | Large black carpenter ants, winged carpenter ants, odorous house ant trails | Foraging from outdoor nests, or a satellite nest in moist wood |
| Spring and early summer | Blacklegged and American dog ticks after time outdoors | Tick checks and prompt removal; see a doctor about symptoms |
| July to hard freeze | Spotted lanternfly adults on trees, decks and walls | Outdoor plant pest; it cannot bite or sting |
| Late summer to early fall | Western conifer seed bugs and boxelder bugs on sunny walls | Seal gaps now, before they get in |
| September to October | Brown marmorated stink bugs gathering on siding | Seeking overwintering sites; exclusion is the fix |
| October onward | Asian lady beetles swarming south and west walls; cluster flies | Same: seal and vacuum, do not spray indoors |
| Fall and early winter | Camel crickets in basements and crawl spaces | Damp, dark areas; reduce humidity and seal |
Timing comes from Penn State Extension and the Pennsylvania Department of Agriculture, listed in the sources below.
The fall invaders
Penn State’s fact sheets describe five insects that move into Pennsylvania homes to overwinter. Penn State treats them as nuisances rather than structural pests, and its advice for all five is the same: mechanical exclusion. Penn State recommends sealing cracks around windows, doors, siding, utility pipes, behind chimneys and under fascia with good quality silicone or silicone-latex caulk, and repairing damaged screens, before the insects arrive. Our guide to stink bugs and other fall invaders covers the timing in detail.
Brown marmorated stink bug
Accidentally introduced from east Asia, the brown marmorated stink bug was first collected in Allentown in 1998, though Penn State says it probably arrived several years earlier. Adults are about 17 mm (0.66 in), shield shaped, with light bands on the antennae. They search for overwintering sites from September through October and can enter houses in large numbers. Penn State notes they will not reproduce indoors or cause damage, but the smell is obvious if many are crushed or vacuumed.
Multicolored Asian lady beetle
First observed in Pennsylvania in the fall of 1993, these beetles are about 7 mm (9/32 in) long, larger than most native lady beetles. Overwintering behaviour begins around the start of October: on a sunny, warm afternoon after a cold night they gather on south and southwest facing walls. Tens of thousands can collect in attics and wall voids. Penn State says they occasionally bite, their yellow defensive fluid can spot walls, and pets that eat them can get chemical burns in the mouth. Our Asian lady beetle guide covers removal.
Boxelder bugs
Adults are brownish black, about 12 mm long, with reddish orange stripes on the thorax and wing edges. Problems are worst near boxelder trees. In fall they congregate on the south side of trees, buildings and rocks exposed to the sun, then try to get into cracks in walls. See our boxelder bug guide.
Cluster flies
Cluster flies arrive at the sunny sides of homes in autumn and can fly about indoors, often in great numbers, throughout the winter. Their larvae develop inside earthworms, not in the house. Penn State says they will not damage your home and are not known to carry diseases of medical importance, though they may leave small dark spots on windows.
Western conifer seed bug
About 3/4 inch (19 mm), reddish brown to dark brown, this pine and spruce feeder was first detected in Pennsylvania in 1992. It gathers on buildings in late summer and early fall. Penn State notes only a single bite has ever been recorded worldwide and the bug is not considered a medical risk.
What not to do once they are inside
Penn State advises against insecticide treatments of wall voids and attics after these insects are inside, because carpet beetles can feed on the dead insects and then move on to woolens and stored goods. It also notes that foggers may kill the insects gathered on walls but will not stop more emerging shortly afterwards. A vacuum and caulk around baseboards, window trim and ceiling fixtures are the indoor tools. Our guide to bugs in the house in winter covers what keeps appearing after the first frost.
Spotted lanternfly
The spotted lanternfly, an invasive planthopper from Asia, was first discovered in Pennsylvania in Berks County in 2014, according to the Pennsylvania Department of Agriculture. It is now the most photographed household pest taxon in our Pennsylvania count by a wide margin. Penn State’s management guide says there is one generation a year: eggs are laid from September to December on trees, decks, houses and outdoor equipment, hatch from late April to June, and adults appear in July and stay active until hard freezes. Adults are about an inch long.
Spotted lanternflies cannot bite or sting, and they are a plant pest rather than a house pest. The sticky honeydew they excrete can coat patio furniture and cars below heavy feeding and grow sooty mould. The state quarantine, which addenda have extended to more counties, asks people to inspect vehicles, trailers and outdoor items before moving them within or out of quarantined areas. Our spotted lanternfly treatment guide explains when treatment is worth paying for.
Ants and termites
Black carpenter ants
Penn State calls the black carpenter ant a common invader of homes in the northeastern United States. Workers are dark, shiny brown to black and 1/4 to 1/2 inch long; winged forms reach 3/4 inch. Large black ants inside are usually the first sign, but the nest may be outside, and the workers mostly forage at night. They seldom tunnel into dry, sound wood, preferring moist, rotting wood and foam insulation board for satellite nests. Finding and fixing the moisture, and finding the parent nest, which is often in a tree, log or waste wood within 100 yards, is the core of control.
Odorous house ants
These are small, 1/16 to 1/8 inch (2.4 to 3.3 mm), brown to black ants that give off a rotten odour when crushed. They prefer sweets, travel in rapid single files, and nest outdoors under rocks and boards or indoors near moisture and warmth. Penn State recommends baits designed for sweet-loving ants, because the workers carry bait back to the colony.
Eastern subterranean termites
Penn State says eastern subterranean termites are present throughout Pennsylvania and often damage structural timbers. In late winter or early spring, black winged swarmers may appear in infested buildings, attracted to light around doors and windows. Swarming termites or their shed wings alone are a sure sign termites are working in the building. In Pennsylvania most infestations are in basement or cellar areas and the timbers just above the cellar walls. Penn State suggests getting estimates from at least three licensed pest control companies. The quickest way to separate a swarmer from a winged ant is the waist: narrow in ants, broad in termites.
House centipedes and camel crickets
The house centipede has a 1 to 1.5 inch body but looks three to four inches long with its 15 pairs of banded legs. Penn State says it was first recorded in Pennsylvania in 1849, cannot survive Pennsylvania winters outdoors, but reproduces in heated buildings. It is harmless and eats other arthropods, so large numbers may point to another pest problem. Our house centipede guide covers reducing them.
Camel crickets, also called cave crickets, are crickets that University of Maine Cooperative Extension describes as accidental invaders attracted to cool, dark, moist areas such as basements, crawl spaces, garages and laundry areas. Our national iNaturalist seasonality index shows when they are most noticed: it climbs from 119 in September to a peak of 250 in November.
Ticks and Lyme disease
Ticks are not house bugs in the strict sense, but they are the Pennsylvania pest with the most health weight. In CDC’s 2023 surveillance data, Pennsylvania reported 16,671 Lyme disease cases, second only to New York with 22,173, out of 89,468 nationwide. The blacklegged tick is the vector. Our national seasonality index for ticks peaks in May at 227, with June close behind. Our tick identification guide shows the blacklegged tick next to the American dog tick and lone star tick. For symptoms after a bite, see a doctor; CDC publishes detailed guidance.
Black bugs in Pennsylvania
When Pennsylvanians search for black bugs indoors, the usual answers are black carpenter ants, odorous house ants, swarming termites in spring (which are black, unlike the cream coloured workers), boxelder bugs with their red markings, and cluster flies at sunny windows. Outdoors in summer, spotted lanternfly nymphs are black with white spots before turning red in their last stage.
What Pennsylvanians actually photograph
We counted iNaturalist research-grade records in Pennsylvania for a fixed list of household pest taxa. These are photographed, identified sightings, mostly outdoors, so they show how often each animal is noticed rather than how many homes are infested.
The spotted lanternfly dominates with 19,217 records, equal to 250.5 for every 10,000 insect records in the state. The Asian lady beetle follows at 11,689, then millipedes (7,790) and carpenter ants (5,052). Boxelder bugs (3,402) and brown marmorated stink bugs (3,306) are close together. House centipedes have 1,797 records in Pennsylvania against just 5 in our Florida count. Blacklegged ticks (1,265) and American dog ticks (1,232) are almost level.
When DIY is enough, and when to call
- Stink bugs, lady beetles, boxelder bugs, cluster flies, seed bugs: seal in late summer, vacuum what gets in. Penn State says exterior insecticide applications by a licensed operator offer only minor relief where sealing is impossible, because sunlight breaks the residue down within days or a week.
- Odorous house ants: sweet ant baits, following the label.
- Carpenter ants: DIY if foragers are coming in from outside; a professional if there is a nest in the structure.
- Termites: always a licensed professional, with several estimates.
- House centipedes and camel crickets: reduce moisture, seal, and deal with the insects they feed on.
Frequently asked questions
What are the most common house bugs in Pennsylvania?
The ones Pennsylvanians find indoors most are overwintering insects: brown marmorated stink bugs, multicolored Asian lady beetles, boxelder bugs, cluster flies and western conifer seed bugs. Add black carpenter ants, odorous house ants, house centipedes, camel crickets and eastern subterranean termites, which Penn State says are present throughout the state. Spotted lanternflies are common outdoors from July to hard freezes.
Why are there stink bugs in my house in winter?
Brown marmorated stink bugs move into walls and attics from September through October to overwinter. On warm winter days they wake and wander into living areas, often from gaps around baseboards, window trim and ceiling fixtures. Penn State says they do not reproduce indoors or cause damage. Vacuum them, seal the gaps, and plan exterior sealing for late summer.
When do termites swarm in Pennsylvania?
Penn State says swarms of black, winged eastern subterranean termites may be noticed in infested buildings during late winter or early spring. They are attracted to light and gather around doors and windows. Swarmers or shed wings indoors are a sure sign of termites working in the building, most often in basement or cellar timbers, and call for a licensed inspection.
Can spotted lanternflies hurt people or pets?
Penn State says spotted lanternflies cannot bite or sting; they feed on plant sap through a straw-like mouthpart. Their main nuisance around homes is honeydew, a sugary excretion that coats surfaces below heavy feeding and grows sooty mould. Egg masses laid on houses, decks and outdoor equipment from September to December can be destroyed, which the Pennsylvania Department of Agriculture says helps reduce local populations.
Is Lyme disease common in Pennsylvania?
Yes. In CDC’s 2023 surveillance data Pennsylvania reported 16,671 Lyme disease cases, the second highest of any state after New York. The blacklegged tick spreads it, and our national seasonality index for ticks peaks in May. CDC publishes guidance on prevention and symptoms, and anyone who feels unwell after a tick bite should see a doctor.
Sources
- Penn State Extension, Brown Marmorated Stink Bug (revised 2017).
- Penn State Extension, Multicolored Asian Lady Beetle.
- Penn State Extension, Boxelder Bug.
- Penn State Extension, Cluster Flies.
- Penn State Extension, Western Conifer Seed Bug.
- Penn State Extension, Spotted Lanternfly Management Guide, and Spotted Lanternfly: What to Look For.
- Pennsylvania Department of Agriculture, Spotted Lanternfly and SLF Quarantine and Permitting.
- Penn State Extension, Carpenter Ants; Odorous House Ant; Eastern Subterranean Termites; House Centipedes.
- University of Maine Cooperative Extension, Camel Cricket.
- Centers for Disease Control and Prevention, Lyme Disease Cases by State or Locality, 2008 to 2023 surveillance data.
- The Pest Control Brief analysis of iNaturalist research-grade records, pulled October 2026.
