Silverfish in the Bathroom
By Marcus Ellery, Pest Control Editor · Updated October 2026 · General information, not an inspection or a diagnosis
A shiny, carrot-shaped insect about half an inch long that runs for cover when the bathroom light comes on matches the UC IPM description of a silverfish. They are night insects that need warm, very humid air, which is why bathrooms suit them. UC IPM puts drying the room out and finding leaks ahead of any pesticide, and suggests sticky traps to see how many there are.
What people usually describe
- A silver or gray insect with a tapered body, seen in the tub, sink or along the baseboard after dark.
- Two long antennae at the front and three bristle-like tails at the back.
- It wriggles fast, almost fish-like, and disappears into a crack.
- Small irregular holes or scraped patches on wallpaper, paper towels or cardboard stored under the sink.
What UC IPM says about silverfish and firebrats
Silverfish and their relative the firebrat are the two insects that fit this description. These are the conditions and food sources UC IPM lists for them.
Silverfish
Shiny silver or pearl-gray, slender, wingless and soft-bodied, about half an inch long and up to three-quarters of an inch, with two long antennae.
Source: UC IPM
Firebrats
Mottled gray or brown instead of silver, and drawn to very warm, drier spots above 90°F, so they favor the hottest parts of a house over a damp bathroom.
Source: UC IPM
Why the bathroom
Silverfish do best between 71 and 90°F and, at the warm end of that range, need relative humidity above 75%. A bathroom after a shower meets both.
Source: UC IPM
What they eat
Starchy and glued materials: paper, wallpaper paste and sizing, book bindings, starch in clothing, cereals, flour, pet food, dust and dead insects. Their mouthparts are weak, so they scrape surfaces rather than bite through them.
Source: UC IPM
How to find out
- 1
Set sticky traps overnight
UC IPM suggests cockroach-type sticky traps for detecting and monitoring silverfish. Place them along the tub, behind the toilet and under the sink, and count what you catch over a few nights. (UC IPM)
- 2
Measure the humidity after a shower and the next morning
If the room stays well above the humidity silverfish need, the fan, the window or a dehumidifier is the first fix. A room that dries quickly points to another source nearby, such as a leak inside the vanity. (UC IPM)
- 3
Look for the leak
UC IPM lists repairing plumbing leaks and drips and keeping shower stalls dry as core steps. Check under the sink, around the toilet base and the caulk line of the tub. (UC IPM)
- 4
Get a free or low-cost identification
Most state Cooperative Extension services, run through land-grant universities, will identify an insect from a specimen or a clear photo, often free or for a small fee. Some university labs, such as Cornell’s Insect Diagnostic Laboratory, take public submissions directly. Find your state’s land-grant university through the USDA NIFA land-grant university directory.
Try this while you wait
UC IPM names sticky traps for monitoring and dehumidifiers for closed, damp spaces. A hygrometer tells you whether the dehumidifier is needed. These are screening and interim tools only. None of them identifies the pest for you or stands in for a licensed professional or an extension identification. As an Amazon Associate we may earn from qualifying purchases. It never changes your price.
When to stop and call a licensed pro
- Traps keep filling after the room has been dried out for several weeks. A pest professional can look for harborage inside walls and cabinets.
- Stored papers, books or clothing show feeding damage. UC IPM lists these materials as food, so move them to dry storage while you sort out the source.
- There is water damage you cannot trace. That is a plumbing or building question first.
If it turns out you need treatment
National 2026 planning ranges from our calculators for the jobs this page most often leads to. Open one to price your own home. Not quotes, and not lab-tested.
| Job | Typical 2026 range |
|---|---|
| Exterminator cost calculator | $150 to $600 |
| Monthly Pest Control Plan cost calculator | $400 to $900 |
Local help
We do not recommend or rate pest control companies. Two neutral places to start:
- State pesticide regulatory agencies (NPIC directory): the state agencies that certify pesticide applicators. EPA advises confirming a pest control company’s license is current before hiring.
- USDA NIFA land-grant university directory: filter by state to reach your Cooperative Extension service, which can identify a specimen.
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Related identification guides
Frequently asked questions
Do silverfish bite people?
UC IPM describes their mouthparts as weak and says they scrape at paper surfaces rather than bite. The source does not address people directly, and we will not go beyond what it says.
Silverfish or firebrat: does it matter?
It changes where you look. UC IPM says silverfish want damp, warm rooms, while firebrats want very warm, drier spots above 90°F. If the insect is mottled gray-brown and turns up in the hottest part of the house, drying the bathroom may not affect it.
Why do I only see them at night?
Both insects hide during the day and come out at night to look for food and water, according to UC IPM. Sticky traps left overnight give a better count than daytime searching.
Sources
This page summarizes what the agencies and university extension services listed above publish about this problem. It is general information, not an inspection, a pest identification or medical advice, and it cannot tell you what is in your home. Sources can change; check the linked page before acting on it. PestCost is not affiliated with any agency, university or association cited here. Spotted an error? Send a correction. Product links are Amazon affiliate links; the quote button is a paid Angi referral. Disclosure.