Occasional Invaders in Chicagoland Basements, Closets and Window Wells

Six pests that live outside but keep showing up indoors

Pest professionals use the label occasional invaders for creatures that do not need a house to survive but end up inside one anyway, usually because the yard got too wet, too dry or too cold. In northern Illinois, northwest Indiana and the Kenosha area the list is fairly predictable: the house centipede, silverfish and its warmer-loving cousin the firebrat, the European earwig, the greenhouse or garden millipede, several crickets including the camel crickets that crowd basements, and two species of clothes moth that are really indoor pests but get grouped here because the fix is similar.

What ties them together is moisture and shelter rather than food scraps. None of them spreads disease the way rodents or cockroaches can, and most do not bite. The problem is that they signal a building condition: a foundation that wicks water, a sump pit without a lid, mulch piled against siding, or a cedar chest that has not been opened since the last move. Each pest below gets its own section, because the right treatment for a camel cricket is very different from the right treatment for a clothes moth.

House centipedes: the fast, long-legged hunter on the basement wall

The house centipede, Scutigera coleoptrata, is the one that makes people jump. Adults have fifteen pairs of very long, banded legs and an inch or more of grayish-yellow body with three dark stripes. They run in bursts, freeze, then run again, and they often appear on bathroom walls or drop into a tub at night. Unlike most centipedes, this species can complete its whole life indoors, and individuals can live for several years, which is why a basement that has them tends to keep them.

They are predators. A house centipede eats silverfish, spiders, carpet beetle larvae, young cockroaches and other small insects, so a large population is a sign that there is plenty of prey somewhere in the house. They can bite if handled, and the bite feels roughly like a bee sting, but they are not dangerous and do not damage wood, fabric or food.

In Chicago-area homes they concentrate where humidity stays high: unfinished basements with a floor drain, crawlspaces under additions, the space behind a laundry tub, and the inside of glass-block basement windows where condensation collects. Killing the centipedes you see does little. Lowering humidity, sealing the gaps where they move between floors, and reducing the insects they feed on is what shrinks the population.

Silverfish and firebrats in old plaster, books and attic boxes

Silverfish are wingless, carrot-shaped insects about half an inch long, covered in silvery scales, with three bristly tails at the rear. They move with a wriggling, fish-like motion and avoid light. Their close relative the firebrat looks similar but is mottled gray and brown and prefers warmer spots, such as near a boiler, water heater or old furnace. Both are ancient insect groups that can live for years and survive long periods without eating.

They feed on starch and protein: wallpaper paste, book bindings, cardboard, photographs, the sizing in cotton and linen, flour and cereal, and dandruff and skin flakes in dust. Damage shows up as irregular notches or surface grazing on paper, yellowish stains, and tiny pepper-like droppings. In a house with lath-and-plaster walls and decades of boxes in the basement or attic, there is no shortage of food.

Most silverfish complaints in the region come from basements and bathrooms, where relative humidity often runs well above what they need, and from upstairs closets and attics packed with paper. Firebrats tend to turn up around boiler rooms in older two-flats and bungalows. Because they hide inside wall voids, behind baseboards and in cardboard, a successful plan pairs drying the space with targeted dust or bait placements in the voids, and it means swapping cardboard boxes for sealed plastic bins.

European earwigs under mulch, patio pavers and back steps

The earwig found throughout Chicagoland is mostly the European earwig, Forficula auricularia, a reddish-brown insect about five-eighths of an inch long with a pair of pincers, called cerci, at the tip of the abdomen. Males have curved pincers and females have straighter ones. Despite the folklore, they do not crawl into ears. They can give a mild pinch if picked up, and they release a faintly unpleasant odor when crushed.

Earwigs are mostly nocturnal scavengers and part-time plant feeders. They chew ragged holes in hostas, marigolds, dahlias, lettuce and corn silk, and they also eat aphids and decaying matter. By day they pack into tight, damp spaces: under landscape timbers, inside rolled-up hoses, beneath patio pavers and stepping stones, under thick shredded-bark mulch and inside the folds of outdoor cushions.

Indoor sightings usually peak in mid to late summer, after a stretch of heavy rain floods their outdoor hiding spots or a dry spell sends them looking for moisture. They come in under worn door sweeps, through gaps at the sill plate and through the weep holes and cracks of basement window wells. Inside, they rarely survive long or breed. The lasting fix is outside: pulling mulch back from the foundation, raising or removing damp debris, and treating the perimeter band where they gather.

Garden millipedes after a soaking rain

Millipedes are not insects. They are slow, cylindrical arthropods with two pairs of short legs on most body segments, and when disturbed many curl into a tight coil. The species most often reported crawling into homes in the Midwest is the greenhouse or garden millipede, Oxidus gracilis, a flattened brown to nearly black animal about an inch long. Native millipedes in wooded lots can be longer and rounder.

They eat decaying leaves, rotting wood and other organic matter, and they need moisture to live. Lawns heavy with thatch, flower beds with deep mulch, compost piles, and lots backing onto forest preserves or ravines produce large numbers. Mass movements typically happen in late summer and fall, and sometimes after heavy spring rains, when hundreds may climb foundation walls, cross patios and slip under garage doors and basement doors.

Millipedes do not bite or sting. Some species secrete a defensive fluid that can stain skin or carpet and mildly irritate the eyes, so they should be swept up rather than crushed by hand. Indoors they dry out and die within a day or two, which means a house full of millipedes is really reporting a yard full of millipedes. Pros focus on a granular or liquid barrier at the foundation, sealing door thresholds, and advising on mulch depth, gutter discharge and grading so the soil next to the house dries out.

House crickets, field crickets and the camel crickets crowding basements

Three kinds of cricket cause most calls. Field crickets are the shiny black singers in the yard that move inside as nights cool in September. House crickets are lighter, yellowish brown with dark bands on the head, and can breed indoors in warm spots. Camel crickets, sometimes called cave or spider crickets, are humpbacked, wingless and silent, with very long hind legs and antennae. Native camel crickets live here, and the greenhouse camel cricket, a species introduced from Asia, is now common in basements across the eastern and midwestern United States.

Camel crickets are the ones homeowners describe as jumping at them. They startle easily and leap toward movement, which feels aggressive but is just an escape reflex. They gather by the dozens in sump pit areas, under basement stairs, in laundry rooms, window wells and detached garages, and they can chew holes in damp fabric, cardboard and paper. Field and house crickets also chew fabrics, especially soiled ones, and the chirping alone can make a bedroom unlivable.

Crickets are attracted to light at night, so bright porch and garage fixtures pull them toward the house. Indoor control relies on sticky monitoring traps along basement walls to find hotspots, a dehumidifier to make the space less inviting, sealing gaps under doors and around utility lines, and perimeter treatment outside. Switching to warm yellow or sodium-style bulbs near entry doors can noticeably cut the numbers that end up inside.

Webbing and casemaking clothes moths in closets and wool rugs

Clothes moths are the exception in this group, because they live entirely indoors. The webbing clothes moth, Tineola bisselliella, is a small, plain, golden-buff moth with a tuft of reddish hair on its head. The casemaking clothes moth is similar but slightly darker and its larva drags a silk case made from the fibers it eats. Adults are weak fliers that flutter low in dim closets and avoid light, unlike pantry moths, which fly openly around kitchens.

The damage comes from the larvae, which digest keratin, the protein in wool, cashmere, alpaca, silk, feathers, fur and felt. They prefer items that are soiled with sweat or food and left undisturbed. Signs include irregular holes in sweaters and coats, bare tracks across wool rugs, especially under furniture where vacuums do not reach, silken tubes or cases, and sandy frass on closet shelves. Piano felts, wool insulation on old pipes, taxidermy and the felt pads under furniture can host them too.

In Chicago-area homes they show up in cedar-lined closets whose cedar has long since lost its scent, in vintage rugs, and in boxes of winter wear packed away in basements and attics. A professional approach starts with an inspection to locate every infested item, then laundering, dry cleaning or freezing what can be saved, thorough vacuuming of closet edges and rug undersides, pheromone traps to monitor adult males, and targeted treatment of closet cracks and rug edges where labeled products allow.

Why Chicagoland houses are such good habitat

The region's housing stock does a lot of the work for these pests. Brick and frame homes built before World War II often have stone or brick foundations with porous mortar, unfinished basements with floor drains tied into the old sewer system, and below-grade window wells that collect leaves and water. Much of Chicago and the inner suburbs sits on flat, poorly drained clay over a high water table, and older neighborhoods frequently have overloaded combined sewers that back up during heavy storms. A basement that has flooded even once can stay damp for weeks.

Climate adds to the pattern. Humid summers push basement humidity up, while the first hard frosts of fall send crickets, millipedes and centipedes looking for shelter at the same time. Newer subdivisions in DuPage, Kane and Will counties have their own triggers: deep landscape mulch, irrigation systems running against the foundation, and sump pumps discharging right next to the house. In both cases, the signs to watch for are sightings concentrated at the lowest level, insects drowning in sump pits and floor drains, damage to paper or fabric packed below grade, and activity that spikes after storms.

How licensed pros handle a mixed invader problem

In Illinois, anyone applying pesticides for hire must be licensed through the Illinois Department of Public Health under the Structural Pest Control Act, and Indiana and Wisconsin have their own licensing programs. A good visit for occasional invaders starts with identifying which species are present, since a house can have centipedes, silverfish and camel crickets at once. The technician checks the foundation exterior, window wells, door sweeps, the sump area, floor drains, crawlspace access and attic boxes, and often places sticky monitors to see where activity concentrates.

Treatment usually combines a perimeter application outside along the foundation, crack-and-crevice dusts or baits in voids, and moisture recommendations such as running a dehumidifier, capping the sump pit, extending downspouts and pulling mulch back. Clothes moth work is its own process built around finding and cleaning infested textiles. Factors that change the cost of service include how many species are involved, the size of the basement and crawlspaces, the amount of clutter and boxes to work around, whether textiles need special handling, and whether a one-time visit or seasonal follow-ups make sense.

• DIY mistake: fogging the basement. Total-release foggers do not reach wall voids where silverfish and centipedes hide, and they leave residue on everything.
• DIY mistake: piling more mulch against the foundation to fix drainage. It holds moisture where earwigs and millipedes breed.
• DIY mistake: relying on cedar blocks alone for clothes moths. Cedar oil fades quickly and does not kill larvae already in a rug or sweater.
• DIY mistake: spraying every centipede you see. They are eating the other pests, and the population returns until humidity drops.

A seasonal prevention plan for older and newer homes

Timing matters. Spring rains and thaw bring millipedes and the first earwigs, midsummer heat and storms push earwigs and camel crickets inside, late August through October is peak season for field crickets and millipede migrations, and winter is when silverfish, centipedes and clothes moths are most noticeable because heating dries upper floors and everyone is indoors. Use the checklist below before each shift.

• Keep basement relative humidity under about 50 percent with a dehumidifier that drains to a floor drain or sump.
• Fit a sealed lid on the sump pit and a grate or cover on old floor drains.
• Clear leaves from window wells, add covers, and caulk the joint where the well meets the foundation.
• Replace worn door sweeps and garage door bottom seals before late summer.
• Pull mulch and stone back several inches from the foundation and keep plantings trimmed off the siding.
• Extend downspouts and sump discharge lines well away from the house.
• Swap cardboard boxes in the basement and attic for sealed plastic bins.
• Clean wool and cashmere before packing it away for summer, and vacuum under rugs and furniture regularly.
• Use warm yellow bulbs near entry doors to draw fewer crickets.