Silverfish and Earwigs in Ontario Homes: What They Mean and How to Stop Them

Silverfish and earwigs are the two insects Ontario homeowners are most likely to find in a basement in late summer, and they get lumped together for good reason. Neither bites, neither spreads disease, and neither will damage your house structurally. What they will do is tell you something useful: both are moisture pests, and finding them consistently means some part of your home is holding more humidity than it should.

Telling the Two Apart

They look nothing alike once you know what to check.

Silverfish are 12 to 19 mm, teardrop-shaped, and covered in fine metallic-grey scales that give them a silvery sheen. They have long antennae at the front and three thread-like tails at the back, and they move in a quick wriggling motion that genuinely resembles a fish. They cannot climb smooth vertical surfaces, which is why they are so often found stranded in bathtubs and sinks.

Earwigs are 12 to 25 mm, flattened, and reddish-brown to near-black. The unmistakable feature is the pair of forceps-like pincers at the rear. Despite persistent folklore, earwigs do not crawl into ears, and the pincers are used for defence and mating rather than for harming people. A pinch from a large one is possible but harmless.

What They Are Actually Telling You

Both species need high humidity to survive and will dehydrate in dry conditions within days. Their presence is a reasonably dependable signal that somewhere in the building is sitting above roughly 50 per cent relative humidity.

In Ontario homes, the usual culprits are predictable: an unfinished basement without a dehumidifier, a bathroom with a weak or unvented exhaust fan, a laundry room, a slow leak under a sink, poor grading that directs rain toward the foundation, or blocked gutters dumping water beside the wall. Earwigs in particular live outdoors by preference — in mulch, leaf litter and damp soil — and only move indoors when outdoor conditions dry out or when heavy rain floods their harborage.

What Each One Damages

• Silverfish feed on starches and cellulose. That means book bindings and pages, wallpaper paste, cardboard boxes, photographs, natural fabrics like cotton and silk, and dry pantry goods such as flour and cereal. Damage is slow and shows up as irregular surface grazing or small holes.
• Earwigs feed mostly on decaying plant matter and other small insects, and can damage garden seedlings, soft fruit and flower petals outdoors. Indoors they rarely cause damage at all — the complaint is almost always their appearance and their numbers.

Neither insect damages structural wood, wiring or drywall, so there is no urgency in the way there is with carpenter ants or rodents. The reason to act is comfort, stored belongings, and the moisture problem sitting underneath.

Fixing the Conditions

Treatment that ignores humidity does not last. Any spray will reduce the population temporarily, but if the space stays damp, numbers rebuild within weeks from eggs and from outdoor populations. The durable fix is environmental:

• Run a dehumidifier in the basement and hold relative humidity below 50 per cent
• Repair leaking taps, traps and supply lines, however minor they look
• Make sure bathroom and laundry exhaust fans vent outside, not into a joist bay or attic
• Clear gutters and extend downspouts at least 1.5 m away from the foundation
• Re-grade soil so it slopes away from the house rather than toward it
• Pull mulch, leaf litter and firewood back from the exterior walls, which removes the earwig staging ground
• Move books, papers and textiles out of cardboard and into sealed plastic bins
• Seal gaps around basement windows, sill plates and utility penetrations

Where populations are already established, a targeted perimeter and crack-and-crevice treatment alongside those changes clears the existing insects while the drying work prevents the next generation. In Ontario, commercial application of many control products requires a licensed technician under O. Reg. 63/09.

Related Husky services: Common Pest Control covers silverfish, earwigs, centipedes and spiders, our Pest Protection Plan keeps damp-season pests in check year-round, and Ant Control handles the other insect most often found in the same damp spaces.

Frequently Asked Questions