Badger HomeownerWisconsin home guide

What's in Your House, and Should You Worry?

Most bugs that turn up in Wisconsin homes are a nuisance, not a threat. Find what you're seeing by month, what you can do yourself, and the few cases where you need a pro or a call to public health.

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Pest Finder

Pick a month to see what's most likely, or type what you're seeing.

Months show when each pest is most noticed in Wisconsin, based on UW–Madison Extension, DNR and DHS. Pests without months can turn up any time.

Bats

  • All four of Wisconsin's cave bats, including the little brown and big brown bats most likely to be in attics, are state-threatened.(Wisconsin DNR) Killing bats is illegal, and getting them out can't harm them.(Wisconsin DNR)
  • Timing: don't block bats' exits during the maternity season, when pups can't fly. DNR's current pages say June 1 to July 31;(Wisconsin DNR) older DNR material says through August 15.(Wisconsin Bat Program)(Wisconsin DNR) If bats pose a health or safety risk, you can exclude them during the season after filing DNR's health exemption form within five days of starting.(Wisconsin DNR)
  • How: watch at sunset to find where they leave, put up a bat house, add one-way doors, and seal the openings at least a week after the bats are gone.(Wisconsin DNR)(Wisconsin Bat Program) You can do it yourself or hire a pest-control company; no permit of your own is needed.(Wisconsin Bat Program)
  • A bat in the living space is most common in late summer, usually a lost young bat.(Wisconsin DNR) If anyone was asleep or intoxicated in the room, or a child or pet was alone with it, don't let it go. Confine it without crushing it, never with bare hands, and call 608-255-2345, weekdays 8 a.m. to 5:30 p.m.; after hours, keep it contained until morning unless it's an emergency.(PHMDC)(PHMDC) Testing the bat often avoids the need for rabies shots.(Wisconsin DHS)
  • If you're sure nobody had contact, close the interior doors and open a window to the outside.(PHMDC) Bats and skunks are Wisconsin's main wildlife carriers of rabies.(Wisconsin DHS)

Wildlife: What's Legal

  • Landowners can trap raccoons, squirrels, woodchucks, rabbits, fox, coyote, beaver and muskrat on their own land year-round with no license, and box traps can be used in cities any time.(Wisconsin DNR)
  • A live-trapped animal must be killed humanely or released within 24 hours, on private land with that owner's permission. Releasing it on DNR land isn't allowed.(Wisconsin DNR)
  • Skunks, opossums and woodchucks are unprotected, as are chipmunks and meadow voles; landowners can control them when they cause damage.(Wisconsin DNR)(UW–Madison Extension)(UW–Madison Extension) Check any trap at least once every 24 hours.(UW–Madison Extension)
  • Anyone you hire to trap needs a Wisconsin trapping or hunting license and your signed, dated permission.(UW–Madison Extension)
  • Before sealing an attic or chimney, make sure no young raccoons are inside, especially in late spring and early summer. Stuff the hole with newspaper; if it's undisturbed for two days, seal it.(UW–Madison Extension) For a skunk under a porch, sprinkle flour at the entrance, check after dark for tracks heading out, then seal.(UW–Madison Extension)
  • Public Health Madison & Dane County doesn't remove wildlife; it handles bats, bites and animals that are a real health risk. For sick, injured or orphaned wildlife, call the Dane County Humane Society Wildlife Center, 608-287-3235.(PHMDC)

Ticks

  • Wisconsin reported 8,929 Lyme disease cases in 2025, the most on record; 2020 to 2024 averaged about 5,300.(Wisconsin DHS) Deer ticks live in every county and are most active May to November.(Wisconsin DHS)
  • Deer ticks carry Lyme and several other diseases. American dog ticks are common but very rarely spread disease here, and lone star ticks are rare.(Wisconsin DHS)
  • Removing a tick: grab it close to the skin with fine-tipped tweezers and pull straight out with steady pressure. Don't twist, crush, burn or smother it.(CDC) See a doctor for fever, rash, aches or fatigue within 30 days of a bite.(Wisconsin DHS)
  • Prevention: use DEET, picaridin, oil of lemon eucalyptus or IR3535; treat clothes, never skin, with permethrin; shower within two hours of coming in.(Wisconsin DHS) Ten minutes in a hot dryer kills ticks on dry clothes.(CDC)
  • In the yard: mow often, clear leaf litter and brush, and put a 3-foot strip of wood chips or gravel between lawn and woods.(CDC)

Bed Bugs

  • Bed bugs are small, flat, reddish-brown insects that feed only on blood. They don't spread disease.(Wisconsin DHS) Look for blood or black spots on mattress seams and headboards.(UW Insect Diagnostic Lab)
  • Confirm what it is first; Extension identifies bugs for free. Then cut clutter, vacuum and seal the bag outside, run bedding through a hot dryer, and encase the mattress and box spring.(EPA) Heat above 115°F kills them.(UW Insect Diagnostic Lab)
  • UW strongly recommends a professional, and two or three follow-up treatments are common.(UW Insect Diagnostic Lab) Never use an outdoor pesticide indoors.(EPA)
  • Renters: ask the landlord to hire a pest company. If they won't, call Madison Building Inspection, 608-266-4551.(PHMDC) Housing providers must keep buildings free of insects and rodents, and an inspector has to see the problem in person.(City of Madison)
  • Skip curbside mattresses and furniture.(UW Insect Diagnostic Lab)

Carpenter Ants and Termites

  • Carpenter ants draw more complaints than any other Wisconsin insect. They don't eat wood; they nest in wood already softened by water, so the real damage is usually the leak.(UW–Madison Extension)
  • A few ants in spring are scouts from outside. Signs of a nest indoors: ants inside between November and early March, many winged ants, sawdust-like debris, or 15 or more workers a day away from the kitchen.(UW–Madison Extension)
  • Find the nest and fix the moisture; replacing wet wood often solves it. Use baits made for carpenter ants. Surface sprays don't reach the queen, and foggers don't work.(UW–Madison Extension)
  • Termites are rare in Wisconsin, found in isolated pockets, and do damage slowly.(UW Insect Diagnostic Lab) UW's lab has seen them from Dane County, almost always brought in on infested landscape timbers or railroad ties. Treat only when active termites are found, and get two or more opinions.(UW Insect Diagnostic Lab)

Fall Invaders

  • Boxelder bugs show up from fall into spring, especially on sunny September and October days. Harmless. Caulk gaps, fix screens and vacuum the ones that get in.(UW–Madison Extension)
  • Asian lady beetles are harmless but can stain and trigger allergies in a few people; vacuum or sweep them up.(UW–Madison Extension) Stink bugs smell and stain when crushed; Wisconsin cases usually involve fewer than 100 bugs.(UW–Madison Extension)
  • Cluster flies pose no health risk and can't breed indoors. Seal and screen before mid-September.(UW–Madison Extension)
  • Exterior sprays only work if they go on before the bugs move in, in September or early October. UW suggests hiring a pro for them.(UW–Madison Extension)(UW–Madison Extension)

Wasps and Hornets

  • Yellowjacket stings from mowing over ground nests happen every August and September.(UW Insect Diagnostic Lab) Bald-faced hornets build paper nests that can approach basketball size.(UW Insect Diagnostic Lab)
  • Colonies die out in fall. If a nest is out of the way, a few hard frosts will finish it.(UW Insect Diagnostic Lab)
  • If a nest has to go, treat it in late evening or at night. Nests in walls, attics or tight spaces are a job for a professional.(UW–Madison Extension)

Mice

  • Mice fit through a hole the width of a pencil. Seal small gaps with steel wool held in by caulk or foam, and bigger ones with hardware cloth or sheet metal.(CDC)
  • Cleaning up: never sweep or vacuum droppings. Air the space out for 30 minutes, wear gloves, soak droppings with 1 part bleach to 9 parts water for 5 minutes, wipe up with paper towels and double-bag them.(CDC)
  • Public Health Madison & Dane County says not to use glue traps, and to keep bait away from kids, pets and wildlife.(PHMDC)

Spongy Moth and Jumping Worms

  • Spongy moth (formerly gypsy moth) caterpillars can strip trees in spring.(DATCP) Dane County is one of 56 quarantined counties, which matters when you move: check patio furniture and other outdoor items for egg masses.(DATCP)(DATCP)(DATCP)
  • Scrape egg masses into soapy water from mid-October to mid-April; band trees in late April; spray Bt in May while caterpillars are small. For valuable trees, consult a certified arborist.(UW–Madison Extension)
  • Jumping worms are a restricted invasive species, so moving them is illegal.(Wisconsin DNR) Bag and trash any you find, don't move soil or mulch off your property, and clean tools and shoes.(Wisconsin DNR) More in the yard calendar.

Hiring a Pro

  • Anyone applying pesticides for hire in Wisconsin needs state certification, a commercial applicator license and a business license from DATCP.(DATCP) Ask to see them.
  • Doing it yourself? Pesticide labels are legally enforceable: use a product labeled for that pest and that place, exactly as directed.(EPA)
  • West Nile virus risk from mosquitoes peaks in August and September; empty standing water around the yard.(Wisconsin DHS)

Free Bug ID

UW–Madison's Insect Diagnostic Lab identifies insects by mail, email with photos, or walk-in at 1630 Linden Drive, 240 Russell Labs, Madison.(UW Insect Diagnostic Lab)(UW Insect Diagnostic Lab) UW Extension lists it as free.(UW–Madison Extension)

Questions

What should I do if a bat is in my house?

If the bat was in a room with someone sleeping or intoxicated, or alone with a child or pet, don't let it go. Without touching it bare-handed or crushing it, confine it and call Public Health Madison & Dane County at 608-255-2345 so it can be tested for rabies. If you're sure nobody had contact, close the interior doors and open a window so it can leave.

When can I get bats out of my attic in Wisconsin?

Not during the maternity season, when pups can't fly. DNR's current pages say no exclusions from June 1 to July 31; older DNR material says through August 15. Outside that window you can exclude bats yourself or hire someone, with no permit of your own. Killing bats is illegal.

Do I need a license to trap a squirrel or raccoon on my property in Wisconsin?

No. Landowners can trap raccoons, squirrels, woodchucks, rabbits and some other animals on their own land year-round without a license, and box traps can be used in cities. A live-trapped animal must be killed humanely or released within 24 hours on private land with the owner's permission, never on DNR land.

Are there termites in Madison?

Rarely. UW's Insect Diagnostic Lab has seen termites from Dane County, almost always brought in on infested landscape timbers or railroad ties. UW advises treating only when active termites are found and getting two or more opinions, since damage happens slowly.

Why do I have boxelder bugs in my house?

They gather on sunny south and west walls in fall and slip into gaps to spend the winter. They're harmless. Caulk gaps, fix screens, and vacuum up any that get inside.

How common is Lyme disease in Wisconsin?

Wisconsin reported 8,929 Lyme cases in 2025, the most on record, and deer ticks live in every county. See a doctor for fever, rash or aches within 30 days of a tick bite.