Bugs That Invade Homes in Fall
As temperatures drop, these bugs look for a way inside. This guide covers 23 of them.
Quick list
- American Cockroach
- Argentine Ant
- Asian Lady Beetle
- Blow Fly
- Boxelder Bug
- Brown Marmorated Stink Bug
- Brown-Banded Cockroach
- Clover Mite
- Drain Fly
- Fruit Fly
- Fungus Gnat
- German Cockroach
- House Centipede
- House Fly
- Longhorn Crazy Ant
- Millipede
- Pharaoh Ant
- Silverfish
- Smokybrown Cockroach
- Western Conifer Seed Bug
- Booklouse
- Camel Cricket
- House Cricket
How to narrow it down
Narrow it down with three quick checks. Count the legs: insects have six, spiders and ticks have eight, and centipedes and millipedes have many more. Check for wings, even folded ones. Then compare size against a coin: a US penny is 19 mm across. Our bug identifier tool does this filtering for you.
The 23 bugs
American Cockroach
American CockroachPeriplaneta americanaThe largest common house cockroach, a reddish-brown roach that lives in sewers, basements and steam tunnels. It can fly short distances in warm weather.
Tell-tale sign: Large reddish-brown body up to two inches long. Risk: American cockroaches can spread bacteria to food and trigger allergies and asthma.
Argentine Ant
Argentine AntLinepithema humileA small, light-to-dark brown ant that forms huge, cooperating supercolonies. Wide, busy trails often stream into kitchens during hot or rainy weather.
Tell-tale sign: Uniform light-brown body with one flat node. Risk: Argentine ants don't sting and rarely bite; they protect aphids and scale insects on garden plants.
Asian Lady Beetle
Asian Lady BeetleHarmonia axyridisAn imported lady beetle that ranges from pale orange to red with anywhere from zero to 19 spots. In fall it gathers in large numbers on sunny walls and slips indoors to spend the winter.
Tell-tale sign: Orange to red dome-shaped body with a variable number of spots. Risk: They can give a mild pinch and release a yellow, smelly fluid that stains, but they carry no disease.
Blow Fly
Blow FlyLucilia sericataA shiny, metallic green or blue fly that lays eggs on dead animals, meat and garbage. A sudden swarm indoors often signals a dead mouse or bird in a wall or attic.
Tell-tale sign: Metallic green, blue or bronze body. Risk: Blow flies don't bite but can carry bacteria from rotting material.
Boxelder Bug
Boxelder BugBoisea trivittataA black bug with red-orange lines on its back that feeds on the seeds of boxelder and maple trees. Large groups sun themselves on warm walls in fall before crawling inside.
Tell-tale sign: Black body with three red lines on the thorax. Risk: Boxelder bugs rarely bite and are harmless, but their droppings can stain curtains.
Brown Marmorated Stink Bug
Brown Marmorated Stink BugHalyomorpha halysA shield-shaped, mottled brown bug that invades homes in fall to overwinter and feeds on fruit and vegetables in summer. It releases a sharp odor when disturbed or crushed.
Tell-tale sign: Shield-shaped, marbled brown body. Risk: Stink bugs don't bite or sting people; they are a household and crop nuisance.
Brown-Banded Cockroach
Brown-Banded CockroachSupella longipalpaA small cockroach with two light bands across its back that prefers warm, dry spots high in rooms. It hides behind picture frames, in electronics and inside furniture.
Tell-tale sign: Two pale yellow bands across the wings and abdomen. Risk: They carry bacteria and allergens like other cockroaches but are not known to bite.
Clover Mite
Clover MiteBryobia praetiosaA tiny, red-brown mite that crawls by the thousands onto sunny walls and windowsills in spring and fall. Crushed mites leave red stains.
Tell-tale sign: Pinhead-size red to brown dots moving on walls. Risk: Clover mites don't bite people or damage homes; they're a staining nuisance.
Drain Fly
Drain FlyClogmia albipunctataA small, fuzzy, moth-like fly that rests on bathroom walls near sinks, tubs and floor drains. Its larvae live in the slimy film inside drains.
Tell-tale sign: Fuzzy, gray, leaf-shaped wings held roof-like over the body. Risk: Drain flies don't bite and aren't known to spread disease in homes.
Fruit Fly
Fruit FlyDrosophila melanogasterA tiny, tan fly with bright red eyes that hovers over ripe fruit, drains, trash and spilled drinks. It can go from egg to adult in about a week.
Tell-tale sign: Very small tan body with bright red eyes. Risk: Fruit flies don't bite; they can carry bacteria from trash onto food.
Fungus Gnat
Fungus GnatBradysia spp.A tiny, dark, mosquito-like fly that hovers around houseplants and windows. Its larvae live in moist potting soil and feed on fungi and roots.
Tell-tale sign: Delicate dark body with long legs and antennae. Risk: Fungus gnats don't bite; larvae can damage seedlings and young roots.
German Cockroach
German CockroachBlattella germanicaA small, light-brown cockroach that breeds rapidly in kitchens and bathrooms, especially in apartments and restaurants. Females carry their egg case until it is ready to hatch.
Tell-tale sign: Light tan to brown body about half an inch long. Risk: German cockroaches contaminate food, and their droppings and shed skins are a major asthma trigger.
House Centipede
House CentipedeScutigera coleoptrataA fast, yellowish-gray centipede with 15 pairs of very long legs that races across floors and walls at night. It hunts silverfish, cockroaches and spiders.
Tell-tale sign: Fifteen pairs of long, banded legs. Risk: House centipedes rarely bite; a bite feels like a mild bee sting.
House Fly
House FlyMusca domesticaThe most common fly in homes, a dull gray fly with four dark stripes on its thorax. It breeds in garbage, manure and rotting food and lands on nearly everything.
Tell-tale sign: Four dark lengthwise stripes on a gray thorax. Risk: House flies don't bite, but they can carry bacteria that cause food poisoning.
Longhorn Crazy Ant
Longhorn Crazy AntParatrechina longicornisA dark, slender ant with extremely long legs and antennae that runs in fast, jerky, seemingly random paths. It nests in soil, trash and wall voids, mostly in warm southern states.
Tell-tale sign: Long legs and antennae relative to its body. Risk: Crazy ants rarely bite and don't sting; their sheer numbers make them a nuisance.
Millipede
MillipedeOxidus gracilisA slow-moving, cylindrical arthropod with two pairs of legs on most body segments. Millipedes eat decaying leaves and often migrate indoors after heavy rain.
Tell-tale sign: Rounded, segmented body with many short legs. Risk: Millipedes don't bite; some release a fluid that can stain or irritate skin.
Pharaoh Ant
Pharaoh AntMonomorium pharaonisA tiny, pale yellow ant that nests in warm, hidden spots inside walls, cabinets and appliances. Colonies split into new nests when disturbed, which makes them hard to control.
Tell-tale sign: Very small, light yellow to amber body with a darker abdomen. Risk: They don't bite, but in hospitals and kitchens they can carry bacteria onto clean surfaces.
Silverfish
SilverfishLepisma saccharinaA wingless, carrot-shaped insect covered in silvery scales that moves with a fish-like wiggle. It eats paper, glue, starches and fabrics in damp areas.
Tell-tale sign: Silvery-gray, teardrop-shaped, scaly body. Risk: Silverfish don't bite; they damage books, wallpaper and stored papers.
Smokybrown Cockroach
Smokybrown CockroachPeriplaneta fuliginosaA large, uniformly dark mahogany cockroach common in the humid Southeast. It lives outdoors in tree holes, mulch and gutters and flies toward lights at night.
Tell-tale sign: Shiny, uniformly dark brown body with no markings. Risk: Smokybrown cockroaches can carry bacteria indoors from mulch and garbage.
Western Conifer Seed Bug
Western Conifer Seed BugLeptoglossus occidentalisA long, brown bug with flattened, leaf-like expansions on its hind legs. It feeds on pine cones in summer and wanders indoors in fall, buzzing loudly when it flies.
Tell-tale sign: Leaf-shaped flat widenings on the hind legs. Risk: Western conifer seed bugs don't bite or sting; they may release a pine-like odor.
Booklouse
BooklouseLiposcelis spp.A tiny, soft, pale insect that feeds on microscopic mold growing on paper, cardboard and stored food. It thrives in humid rooms and new construction.
Tell-tale sign: Very small, pale, wingless body. Risk: Booklice don't bite and aren't true lice; they indicate high humidity and mold.
Camel Cricket
Camel CricketDiestrammena asynamoraA humpbacked, wingless cricket with very long legs and antennae that lives in basements, crawl spaces and garages. It jumps toward threats, which startles many people.
Tell-tale sign: Arched, humpbacked brown body. Risk: Camel crickets don't bite or spread disease; they point to damp conditions.
House Cricket
House CricketAcheta domesticusA light yellowish-brown cricket with three dark bands on its head that chirps loudly at night. It wanders indoors in fall and can chew fabric and paper.
Tell-tale sign: Yellowish-brown body with dark crossbands on the head. Risk: House crickets are harmless, though they can damage clothing and keep you awake.
Which ones should you worry about?
0 of the 23 bugs in this guide can bite or sting. None of them are considered medically significant. The rest are harmless or simply a nuisance.
Frequently asked questions
What is the most common one?
Among the bugs in this guide, the American cockroach and Argentine ant are the ones people ask about most.
Which of these are dangerous?
None of them are medically significant, though some can bite or sting.
How can I identify a bug I found?
Use the free bug identifier tool: choose the number of legs, wings, main color, size and where you found it, and it will list the closest matches.