Silverfish in Ontario

Overview

Silverfish are teardrop-shaped, silver-grey insects that move with a distinctive wriggling, fish-like dart — the reason for their name. They are among the few nuisance pests that cause genuine property damage: they graze on the starches and sugars in paper, book bindings, wallpaper paste, and natural fabrics, leaving holes and yellow stains behind. In Ontario homes they favour warm, humid, undisturbed spaces — bathrooms, basements, laundry rooms, and the backs of storage closets. Because they breed indoors and can survive months without food, silverfish quietly build populations that persist even in spotless homes. Most Ontario homeowners meet them when they lift a stored box, open an old book, or spot one stranded in a bathtub or sink they can’t climb out of.

Identification

An adult silverfish is 12–19 mm long, flattened, and tapered from a broad head end to a narrow tail, giving it a carrot or teardrop outline. It’s covered in metallic silver-grey scales, has two long antennae at the front, and — the clincher — three long bristle-like appendages projecting from the rear. Its movement is unmistakable: a rapid, side-to-side wriggle across floors and walls.

The closely related firebrat shares the three-tailed shape but prefers hot spots like boiler rooms and the areas around ovens and hot-water pipes. Silverfish, by contrast, seek out the cool damp — which is why Ontario bathrooms and basements are their classic haunts.

Life Cycle

Silverfish develop through gradual metamorphosis: egg, nymph, adult, with no pupal stage. A female lays eggs a few at a time in cracks and crevices, and nymphs hatch looking like miniature, whitish adults that darken to silver as they mature. Development is slow and depends heavily on humidity — in ideal warm, damp conditions it takes a few months, but it can stretch to years in drier spots. Silverfish are unusually long-lived for insects, surviving up to several years and continuing to moult even as adults. That slow, steady reproduction is why infestations creep up gradually rather than exploding, and why they persist once established.

Habitat & Behaviour

Silverfish are nocturnal, moisture-dependent, and shy of light — they scatter when a basement light flicks on. During the day they shelter in tight, dark cracks: behind baseboards, under flooring, inside wall voids, in stacks of stored paper, and beneath sinks. They favour relative humidity above roughly 75%, which is why bathrooms, basements, laundry areas, and poorly ventilated rooms are their strongholds. They can travel throughout a home in search of food but always return to damp harbourage. Clutter — especially paper, books, and cardboard — is doubly attractive because it offers food and hiding space at once.

Diet

Silverfish specialise in polysaccharides — the starches and sugars in everyday household materials. Their menu includes paper and the cellulose in book pages, the starch-based glues in book bindings and wallpaper paste, natural fabrics like cotton, silk, and linen, and pantry staples such as flour and cereal. They’ll also consume dust, dead insects, and organic debris. This broad, starch-heavy diet, combined with an ability to fast for months, is what makes them such durable and destructive occupants of storage areas.

Signs of Infestation

• Live silverfish, often trapped in sinks, tubs, or dry basins they can’t climb out of.
• Irregular holes and notches in book pages, paper, wallpaper, and stored garments.
• Yellow staining or discoloration on paper, fabric, and wallpaper edges.
• Peeling or lifted wallpaper, where they’ve grazed the paste beneath.
• Tiny black pepper-like droppings and scattered shed scales near harbourage.
• Small scrape marks on surfaces where they’ve fed on starchy films.

Damage Caused

Silverfish damage accumulates slowly but can be permanent. On books and documents they chew irregular holes, weaken bindings by eating the starchy glue, and leave yellow stains — a real threat to archives, photos, and collections. On walls they graze wallpaper paste, causing peeling and lifted edges. On textiles they thin natural fibres and leave small holes and stains, particularly in long-stored clothing. None of this is structural, but for anyone storing valuable paper goods or heirloom fabrics in a damp Ontario basement, the losses are avoidable and worth preventing.

Health Risks

Silverfish pose essentially no direct health risk. They don’t bite, sting, or transmit disease, and they aren’t venomous. The one indirect concern is that their shed scales and droppings can contribute to household dust and, in rare cases, trigger mild allergy symptoms in very sensitive individuals — a minor issue compared with pests like cockroaches. For restaurants and food-storage businesses, silverfish in dry-goods or paper-storage areas are more a contamination and quality-control concern than a health hazard, but inspectors still expect them controlled.

Seasonal Activity in Ontario

Because silverfish breed indoors, they stay active all twelve months of the year wherever it’s warm and humid — a heated Ontario basement or bathroom never gives them a true off-season. That said, activity often ticks up in summer, when outdoor humidity climbs and indoor dampness peaks, and in late fall when heating systems create warm pockets. Cottage-country homes around Muskoka and Orillia that sit closed and unventilated can develop silverfish problems in damp seasons, discovered only when owners return. Unlike seasonal invaders, silverfish don’t migrate indoors — they’re already there, quietly persistent year-round.

Where They Hide

Bathrooms (behind and beneath sinks, tubs, and toilets), basements (in cracks, under stored boxes, around foundation walls), laundry rooms, kitchen cupboards, attic and closet storage, behind baseboards and wallpaper, inside wall voids, and among stacks of books, magazines, and cardboard. Anywhere that stays dark, damp, and undisturbed is a candidate.

How They Enter Homes

Silverfish often arrive inside infested items — cardboard boxes, secondhand books, stored papers, and old furniture carried up from a damp storage unit or down from an attic. They also migrate from adjoining damp areas and enter through foundation cracks, gaps around plumbing, and utility penetrations. Once inside, they spread through wall voids and along plumbing runs to any room that offers the humidity they need.

Prevention Tips

1. Run a dehumidifier in basements and damp rooms; aim to keep relative humidity below 50%.
2. Fix leaks fast — dripping taps, sweating pipes, and damp foundation walls all feed them.
3. Improve ventilation in bathrooms and laundry rooms with exhaust fans.
4. Store books, documents, and off-season clothing in dry, sealed plastic containers rather than cardboard.
5. Reduce clutter, especially paper and cardboard stacks that offer food and shelter.
6. Seal cracks around baseboards, pipes, and the foundation to cut off harbourage and entry.
7. Vacuum cracks and storage areas periodically to remove eggs and shed scales.

A dehumidified, decluttered storage area removes the two things silverfish need most — moisture and food. Our DIY pest prevention guide covers the whole-home version.

DIY vs. Professional Treatment

You can knock down visible silverfish with cleaning, traps, and desiccant dusts, and lowering humidity is the single most effective thing a homeowner can do. But cleaning doesn’t reach the eggs and hidden populations tucked into wall voids, under flooring, and behind fixtures, so infestations tend to return. Professional treatment targets silverfish at all life stages, applies residual products into the cracks where they harbour, and — most importantly — identifies the moisture source keeping them alive. Sani IQ addresses both the pest and the dampness behind it and backs the work with a Pest-Free-Or-It’s-Free guarantee. See our silverfish control service for details, or read the full silverfish diet breakdown.

References

• Health Canada — Silverfish and Firebrats
• University of Minnesota Extension — Nuisance Insects

Last updated: July 16, 2026 · Reviewed by Sani IQ licensed technicians