Bugs in Firewood: How to Keep Them Out of Your House This Fall

Quick answer: Almost every insect that comes in on Ontario firewood is a passenger, not an invader — carpenter ants, wood-boring beetles, spiders, and the occasional overwintering wasp queen. Two rules solve the large majority of it: stack the wood off the ground and well away from the house, and bring in only what you will burn that day. Never spray firewood with insecticide — you will be breathing whatever you applied. And never move firewood between regions, which is how invasive forest pests travel. The one sighting worth acting on is carpenter ant activity indoors in the middle of winter, because that points at a nest inside the building rather than in the woodpile.

What actually rides in on firewood

The panic that sends most people searching this is termites. Set that aside first. Termites are present in parts of southern Ontario but are uncommon through cottage country and the northern GTA, they do not typically arrive in seasoned firewood, and the insects people mistake for them in a wood stack are almost always something else.

Here is what is genuinely in the pile:

Carpenter ants. By far the most common and the only one with real consequences. They do not eat wood — they excavate galleries in wood that has already been softened by moisture, which describes a great deal of firewood that has sat on the ground. A split log can carry a live satellite colony inside it.

Wood-boring beetles. Longhorned beetles, metallic wood borers, powderpost beetles. Their larvae develop under the bark or in the sapwood. Bring a log indoors, warm it to room temperature, and adults emerge days or weeks later — often loudly. They are dramatic, and almost entirely harmless: the species that develop in firewood are not interested in the dry, finished lumber of your house.

Spiders. A stacked woodpile is excellent spider habitat. They come in on the wood, disperse, and are mostly a nuisance issue.

Overwintering wasp and hornet queens. Fertilized queens seek out sheltered crevices in autumn and a bark gap qualifies. Warm one indoors in January and she wakes up, confused, in your living room.

Sowbugs, millipedes and centipedes. Common, moisture-driven, harmless, and generally dead within a day or two indoors because your house is far too dry for them.

Almost none of this population can establish itself in your home. The logs are their habitat; your house is not.

The two rules that solve most of it

Rule one: stack it off the ground, away from the house

Wood in direct contact with soil wicks moisture, and damp wood is what carpenter ants want. Get it up on a rack, pallets, or cinder blocks so air moves underneath.

Then move the pile away from the building. Six metres is a reasonable target. A woodpile stacked against the siding is a covered, humid bridge running directly from the yard into the wall cavity, and it is one of the more common reasons a Muskoka cottage or a Barrie home ends up with carpenter ants in the structure rather than merely in the woodpile.

Cover the top of the stack to shed rain, but leave the sides open. A tarp wrapped over the whole pile traps humidity and creates precisely the conditions you are trying to avoid.

Rule two: bring in only what you will burn today

This single habit does more than anything else on this list. Insects in firewood become a problem when the wood warms up indoors — cold, dormant insects revive at room temperature and start moving. Wood that goes from the stack to the fire within a few hours never gets the chance.

Stop stacking a week’s supply beside the woodstove. If you need an indoor buffer, keep it in an unheated garage or mudroom rather than the living space.

Two supporting habits: knock each log hard against something outside before carrying it in, which dislodges a surprising amount, and do not store kindling in cardboard, which holds moisture and attracts the same insects all over again.

Never spray firewood

This one is not a preference. Insecticide applied to firewood will be vaporized when you burn it, and you will breathe the combustion products in an enclosed room. There is no product on the market — including anything marketed as natural — that is safe to apply to wood destined for a fire.

The correct treatments for firewood are seasoning and time. Wood split, stacked and dried for six to twelve months is substantially less attractive to insects than fresh green wood, because most of the moisture they depend on is gone.

If a stack has become genuinely infested, the answer is to burn through it rather than treat it — and to stack the next load correctly.

Do not move firewood between regions

This one is bigger than your house. Firewood is a primary pathway for invasive forest pests — emerald ash borer, Asian long-horned beetle, hemlock woolly adelgid and others — which is why the Canadian Food Inspection Agency regulates firewood movement out of infested areas and Ontario Parks restricts what you can bring into a park.

The practical rule: buy firewood where you will burn it. Do not carry a trunkload from Oakville up to the cottage, and do not carry the leftovers home again. Local wood is not a formality — it is the single most effective thing an individual can do to slow the spread of pests that kill trees by the millions.

The cottage woodpile, specifically

Seasonal properties around Muskoka, Simcoe County and Bradford concentrate every risk factor at once: wood often stacked against a wall or under a deck, a building sitting cold and unoccupied for weeks, and a structure frequently older, with more gaps than a suburban build.

Three adjustments make a real difference. Move the woodpile off the deck and away from the wall before you close up for the season. Stack it on a rack rather than on dirt or a stone patio. And when you arrive to open in spring, look at the wall nearest where the wood was stacked before you look anywhere else.

The one sighting that matters: carpenter ants indoors in winter

Everything above is largely a nuisance. This is not.

If you are seeing large black ants walking inside during December, January or February — not the day you carried wood in, but repeatedly, weeks apart — that is very unlikely to be firewood. Ants brought in on a log are cold, slow and few. A steady trickle of active ants in the middle of an Ontario winter means a colony somewhere warm, which means inside the structure.

Look for coarse sawdust-like shavings below trim, a hollow sound when you tap around a window frame, and any faint rustling in a wall on a quiet evening. Our carpenter ant library entry covers identification in detail.

Carpenter ants damage buildings slowly and out of sight. The wall they are in is almost always wet — a roof leak, a failed window seal, or years of a woodpile holding moisture against the siding — which means there are usually two repairs waiting, not one. Finding that in February is much better than finding it in May.

What it costs, and the honest recommendation

Every Sani IQ service starts with a $95 professional inspection, credited in full when you book the treatment. For a suspected carpenter ant problem that inspection is the valuable part — locating the nest and the moisture feeding it is the entire job, and treating without finding it is guesswork.

Carpenter Ant treatment is $525. A one-time visit resolves the colony you have.

But treat that as the entry point, not the plan. Firewood arrives every year, the woodpile goes back in roughly the same place, and the gaps that let ants into the wall are still there next spring. Our General Insect Control annual plan at $845/year covers carpenter ants alongside the spiders, beetles and seasonal nuisance insects, with visits timed to the seasons rather than to whenever you notice something. For properties with a woodstove, a cottage, or a wooded lot, that is the difference between one repair and a recurring one. Our Essentials plan at $1,195 adds broader coverage for properties that need it.

Not sure which applies? Take the free quote quiz for a straight answer in about a minute, or call (705) 302-1887. Restaurants, lodges and rental properties burning wood at volume should look at our commercial pest management programs instead, where storage volume changes the calculation entirely.

Sani IQ is BBB Accredited, carries $5M liability coverage, is licensed under the Ontario Pesticides Act and registered with the MECP, and holds a 5.0 rating across 126 Google reviews. Our technicians are employed, licensed and background-checked — never subcontracted.

Frequently asked questions

Can I spray my firewood to kill the bugs? No. Whatever you apply will be released when the wood burns, into the room you are sitting in. Season the wood, stack it properly, and bring in only what you will burn.

Should I stack firewood in the garage? An attached garage is not ideal, since it shares walls and often a door with the living space. A detached garage or an outdoor rack is much better. If the attached garage is your only option, keep the stack off the floor, away from the shared wall, and limited to a few days’ supply.

Beetles are emerging from logs beside my stove. Is my house at risk? Very unlikely. Wood-boring beetles that develop in firewood need the moisture content of freshly cut wood, which finished structural lumber does not have. Vacuum them up and move the indoor stack outside.

Can firewood bring termites into my home? It is rare in most of our service area. Termites are present in pockets of southern Ontario but are not a typical firewood passenger. Large winged insects near a woodpile are far more often carpenter ants or flying ants.

How long should firewood season before burning? Six to twelve months for most Ontario hardwood, split and stacked with airflow on all sides. Properly seasoned wood burns hotter, produces less creosote, and is markedly less attractive to insects.

I found a wasp in the house in January. Where did it come from? Most likely an overwintering queen that sheltered in bark and woke up in the warmth. She is alone, will not found a nest indoors, and does not indicate a nest in your house. Repeated sightings over several weeks are a different matter and worth a look.