You switch on the bathroom light at night and a small silvery bug darts under the baseboard. That is a silverfish. It doesn’t bite or spread disease, and its presence mostly tells you one thing about your home: there is too much moisture somewhere. Here is how to recognize it, why it settles in and what actually gets rid of it.
How to recognize it
- Size: just over a centimetre long as an adult.
- Shape: flat, carrot-shaped, wider at the front.
- Colour: shiny silver-grey, covered in fine scales.
- Giveaways: two long antennae at the front and three long bristles at the back. No wings.
- Behaviour: nocturnal, very fast, avoids light.
Its cousin, the firebrat, looks similar but is grey or mottled brown with no silver sheen, and prefers warmth: near the furnace, water heater, oven or in the attic.
Why your house
According to Health Canada, silverfish prefer a relative humidity of 75 to 95%. That is far more than the air in a healthy home. Where they find it:
- a poorly ventilated bathroom, around the tub, shower and sink;
- a damp basement, especially near the laundry area and floor drain;
- slow leaks under the sink or behind an appliance;
- walls and floors above a damp crawl space.
They eat almost anything with starch or cellulose: crumbs, wallpaper paste, book bindings, cardboard, paper, mould and dead insects. They can survive months without food, which is why you keep seeing them long after a big clean-up.
Are they dangerous?
No. Silverfish don’t bite, sting or spread disease. A large, long-standing infestation can damage books, papers, photos, wallpaper or starched fabric. The real warning is elsewhere: if they are thriving, the moisture that draws them can also encourage mould.
How to get rid of them
1. Dry things out
This is the step that solves the problem. Without it, everything else only buys time.
- Run the bathroom fan during and for 20 minutes after every shower.
- Put a dehumidifier in the basement and aim for around 50% relative humidity.
- Fix leaky taps and pipes, and check the caulking around the tub and shower.
- Move boxes and belongings away from basement walls so air can circulate.
2. Remove food and hiding spots
- Vacuum often along baseboards, behind appliances and in the pantry.
- Store papers, books and seasonal clothing in sealed plastic bins rather than cardboard.
- Seal cracks in baseboards, trim and around pipes.
3. Trap them
The simplest trap, described by Health Canada: a glass jar wrapped on the outside with tape, with a little bread or flour inside. Silverfish climb the tape, drop into the jar and can’t climb the smooth glass. Sticky traps along baseboards are mostly useful for measuring activity.
4. Treat the hiding spots
Diatomaceous earth or boric acid dust applied in a thin layer in cracks and voids, where no one walks, works slowly but lasts. Health Canada reminds you to look for the registration (PCP) number on the label, and that an insecticide takes 10 to 14 days to show results. Avoid breathing the dust.
When to call
- You see them every day despite drying things out.
- They are on several floors: they are probably moving through the walls.
- You keep archives, books or valuable documents.
- You suspect a water leak you can’t find.
A technician locates the damp areas and hiding spots, treats the wall voids and tells you what needs fixing. Silverfish often come with house centipedes, which feed on them: see our guide to bugs in the house. For an assessment, contact us or call 514-638-8705. The estimate is free.
Frequently asked questions
Do silverfish come up the drain?
No. They live in cracks, walls and under floors, and come to the drain because it is damp. The ones you find in the tub fell in and can’t climb the smooth sides.
Does a silverfish mean my house is dirty?
No. It means it is damp. They turn up in spotless homes with a poorly ventilated bathroom.
How long does it take to get rid of them?
Once the moisture is fixed, activity drops within a few weeks. Because they live long and breed slowly, you may still see a few for a month or two.