Silverfish in Bathroom: Why They Show Up and How to Dry Them Out

November 6, 2026 · 8 min read

By the PestCodex Editorial Team · Checked against 5 research sources

Silverfish in the bathroom are a sign the room stays too humid: these insects need roughly 75% relative humidity or more, and a steamy bathroom with a weak fan or a slow leak gives them exactly that. Dry the room out and most of the problem goes away on its own.

Silverfish in bathroom: what to do tonight

You can make a difference before you buy anything. Start here.

1. Run the exhaust fan during every shower and after it. The EPA recommends running the bathroom fan or opening a window when you shower. If the fan barely pulls a tissue toward it, it needs cleaning or repair.

   

2. Wipe up standing water. Dry the tub edge, the floor around the toilet, and the sink counter before bed. Hang wet towels and bath mats where they can dry.
3. Look for leaks. Check under the sink, around the toilet base, and at the tub faucet. The EPA says to fix plumbing leaks as soon as possible.
4. Set traps. Wrap a small glass jar with masking tape on the outside and stand it upright where you saw silverfish. They climb the tape, drop in, and can't climb the smooth glass. Sticky traps sold for cockroaches also work.

   

5. Clear the floor. Move stored toilet paper, cardboard, magazines, and old towels out from under the sink and off the floor.

Why silverfish love bathrooms: humidity above 75%

Ohio State University Extension puts silverfish’s preferred range at 75% to 95% relative humidity. UC IPM adds that silverfish prefer 71 to 90°F (22 to 32°C), and at the warmer end of that range, humidity must stay above 75% for them.

A bathroom hits those numbers every day. Hot showers push humidity up fast, and in a small room with no window or a weak fan, it can stay high long after you’re done. Add a dripping trap under the sink or a damp wall behind the tub and you have a permanent water source.

That is why you usually see them in bathrooms, kitchens, laundry rooms, and basements, and why drying works so well. UC IPM notes that dehumidifiers and fans can bring humidity down to a level silverfish can’t tolerate.

Where they come from

UC IPM describes these insects crawling along pipelines and through openings in walls and floors, moving from one level of a building to another. In the bathroom they hide:

• Behind baseboards and loose tiles
• In gaps around pipes under the sink and behind the toilet
• Behind the vanity and inside wall voids
• In cracks in grout and caulk around the tub

Silverfish are nocturnal, which is why you mostly spot them when you switch on the light.

If your whole house smells damp, the problem may be bigger than the bathroom. Our guide to tracking down a musty smell in the house covers how to find hidden moisture.

What silverfish eat in a bathroom

Silverfish eat a wide range of starchy and paper-based materials, and a bathroom has more of them than you might think. UC IPM and Health Canada list:

• Paper products, including the glue and sizing in paper and cardboard
• Wallpaper paste
• Dust, dead insects, and crumbs
• Mold and other fungi growing on damp surfaces
• Starch in fabrics

In a bathroom, that means cardboard toilet paper tubes, stacked rolls, old magazines, damp cardboard boxes under the sink, and mildew in grout lines. Cleaning those up cuts their food supply.

They are also hard to starve. UC IPM and Ohio State both say silverfish can survive several months without food, which is why removing moisture matters more than removing food.

Silverfish vs. firebrats: same shape, different conditions

Two similar insects show up in bathrooms. Both are about 1/2 inch (13 mm) long, with a flattened, carrot-shaped body that tapers toward the rear, two long antennae, and three long tail bristles.

Sources: UC IPM Pest Notes: Silverfish and Firebrats; Ohio State University Extension ENT-64.

The difference matters for control. Drying the room is the main fix for silverfish. Firebrats are driven by heat more than moisture, so look for insulated gaps around hot water lines and the water heater. UC IPM also notes that several boric acid dusts don’t work well on firebrats.

How to get rid of silverfish in the bathroom for good

Once you know the cause, the fix is mostly maintenance.

1. Get humidity under control. Aim for the EPA target of below 60% relative humidity, ideally 30% to 50%. Use the exhaust fan, leave the door open after showers, and add a small dehumidifier if the room still stays damp.
2. Fix every leak and drip. UC IPM recommends fixing leaks and sealing gaps where pipes and conduit pass through walls.
3. Caulk cracks. Re-caulk gaps around the tub, along baseboards, and around pipe openings to remove hiding spots.

   

4. Clean and declutter. Vacuum along baseboards, clean under the sink, and store paper goods in plastic bins.
5. Keep trapping. Check jars or sticky traps every few days. Falling counts mean the drying is working.
6. Treat dry hiding spots only if needed. See the next section.

Health Canada notes that silverfish populations grow slowly, so a large number usually means they have been there for a long time. Expect it to take a few weeks for counts to drop.

Baits, diatomaceous earth, and sprays: what the labels say

For a light infestation, UC IPM says insecticides usually aren’t needed. If you do use a product, it will only work if you also remove the moisture.

Diatomaceous earth (DE). DE is a fine powder made from the fossilized remains of tiny aquatic organisms called diatoms. It isn’t a poison; it absorbs the oils and fats from an insect’s outer shell so it dries out. NPIC notes that DE stays effective only while it is kept dry and undisturbed. That makes it useful in dry wall voids, behind the vanity, and under baseboards, and nearly useless on a wet bathroom floor. UC IPM warns that dust that gets wet and dries again cakes up and has to be reapplied.

• Use a product labeled for indoor insect control, and follow the label. The label is the law.
• Apply a thin, barely visible layer with a bulb duster. UC IPM notes a thick layer just makes surfaces slippery.
• Avoid breathing the dust. NPIC notes it can irritate the nose and airways.

Boric acid and silica gel dusts. These also last a long time in dry voids, according to Health Canada. Products combining silica gel or boric acid with pyrethrins work best when the dust contacts the insects directly (UC IPM).

Baits. Baits sold for silverfish exist, but UC IPM reports they generally aren’t very successful, because silverfish tend not to feed on them. Treat bait as a minor add-on, not the plan.

Sprays. Crack-and-crevice sprays with pyrethrins or pyrethroids can kill silverfish on contact. Spray only into cracks and gaps, not open surfaces, and keep products out of sinks and drains.

What doesn’t work (and why)

Sources: UC IPM Pest Notes: Silverfish and Firebrats; NPIC Diatomaceous Earth Fact Sheet.

Silverfish aren’t dangerous, either. Health Canada calls them harmless to humans, and their jaws are too weak to bite. Panic-buying strong chemicals for a few silverfish usually does more harm than the insects.

When to call a professional

Most bathroom silverfish problems end once the room stays dry. Bring in a pest professional, or a plumber, when:

• Trap counts haven’t dropped after 2 to 3 weeks of drying and treatment. UC IPM says this usually means they’re coming from untreated hiding spots.
• You find silverfish in several rooms, closets, or bookshelves, not just the bathroom.
• You suspect a hidden leak inside a wall or under the floor.
• Walls feel damp or show peeling paint or mold. See our guide to condensation on walls for how to tell condensation from a leak.
• You rent. Report leaks and a broken exhaust fan to your landlord, since those repairs are usually theirs.

If you also find small fuzzy larvae or holes in wool and carpets, that’s a different pest; check our carpet beetle guide.

Bathroom silverfish checklist

• Exhaust fan runs during and after every shower
• Humidity below 60% (30-50% ideal) an hour after showering
• Leaks under the sink, toilet, and tub fixed
• Cracks around tub, baseboards, and pipes caulked
• Paper, cardboard, and old towels off the floor
• Taped jars or sticky traps checked every few days
• Any dust applied thinly in dry voids only, per the label
• No foggers, no drain chemicals