Silverfish In The Bathroom: They Are Telling You About Damp

What they are and what they are not

Silverfish are small, grey, fast, and active at night, which is why people meet them by turning on a bathroom light at two in the morning. They do not bite, they do not carry disease, and they are not a sign that the apartment is dirty.

They do eat starches: paper, cardboard, book bindings, wallpaper paste, and the glue in packaging. In a bathroom they are usually after the humidity first and whatever cellulose is around second.

Read them as a humidity signal

This is the useful part. Silverfish need consistently high humidity, and they leave rooms that dry out. So a persistent population is information: something in that room is staying wet.

Common sources in an apartment bathroom are an extractor fan that does not move air, a slow leak under the sink, a failed silicone seal letting water behind the tub, and a windowless room where showers are not ventilated. Finding which one applies matters more than any treatment.

What to do first

• Dry the room out properly: run the fan long after showers, squeegee, leave the door open, and use a dehumidifier if the room stays damp.
• Check under the sink with a dry paper towel along the pipes and the cabinet floor.
• Remove the cellulose: cardboard boxes, paper packaging, old magazines, anything stored under the sink in a box.
• Vacuum the corners, the gap behind the toilet, and the edge where the floor meets the wall, which is where eggs sit.
• Fill obvious gaps around pipes with removable putty, since that is both a route in and a damp harbour.
• Move stored paper goods out of the bathroom entirely, spare rolls included.

Two or three weeks of a genuinely drier room usually does more than anything sold for the purpose, because the problem was never the insects.

About sprays and traps

Sticky traps in corners tell you where they are travelling, which is useful. Spraying baseboards is mostly theatre against an animal that lives inside wall voids and comes out at night.

Skip the aerosol foggers in particular. They are ineffective against something that hides in cavities, and in a small windowless room they are unpleasant and unnecessary. This is a humidity problem being treated as a pest problem.

When it belongs to the building

• They keep appearing in a bathroom you are ventilating properly.
• You find them in more than one room, or neighbours have them too.
• There is visible damp: bubbling paint, a soft patch of drywall, staining on the ceiling.
• The bathroom fan does not hold a square of toilet paper against the grille.
• You find damp under the sink or around the tub that returns after drying.

Report those with dates and photographs, and describe the damp rather than the insects. A maintenance request about moisture gets a plumber, and a request about silverfish gets a can of spray.

The clean that supports it

The cleaning that actually helps here is the deep kind: behind and under the vanity, the corners, the seal around the tub, the fan cover, and inside the cabinet where paper goods were stored. Those are the places that stay damp and hold both eggs and food.

That set is inside deep apartment cleaning, and the guide to a bathroom with no window covers the humidity side, which is the half that actually decides whether they come back.