Carpenter Ants vs. Regular Ants: How to Tell If Your House Is in Trouble

Posted on 2026-05-29

That Big Black Ant on Your Windowsill Might Not Be Harmless

You've probably seen them by now. It's late spring, the weather finally turned, and suddenly there are ants showing up inside. Big ones, way bigger than the little guys you find marching across the kitchen counter in July. Maybe a few of them even had wings.

Most people grab a can of spray, knock out the ones they can see, and move on with their day. For most ants, that's fine. But if those big black ants are carpenter ants, spraying the ones you see is a bit like mopping up water without finding the leak. The real problem is somewhere you can't see it, and it's chewing through your house while you're not looking.

Here's how to tell the difference, and why it matters more than you'd think.

How to Spot a Carpenter Ant

Size is the first giveaway. Carpenter ants are some of the biggest ants you'll run into in Ontario, anywhere from about 6 to 13 millimetres. That's roughly the length of a grain of rice up to the size of a small bean. The ants you usually see on your patio or sidewalk are tiny by comparison.

Most carpenter ants around here are solid black, though some have a dark reddish tint on the middle section. If you can get a close look, there are two dead giveaways. Their waist has a single bump where the body narrows, not two. And the top of their back curves in one smooth, even arch instead of looking dipped or uneven. You don't need to be an entomologist to catch this.

The wings throw people off the most. In spring, carpenter ant colonies send out winged “swarmers,” the next generation heading out to start new nests. People see them and assume they've got flying ants or even termites. They're neither. They're just carpenter ants doing what they do every May and June. But here's the part that matters: which side of the wall they're on tells you a lot.

The One Thing That Tells You There’s an Ant Problem

If you see a handful of carpenter ants outside, on the deck, along the foundation, around the woodpile, that's normal. They live outdoors. They're supposed to be there. Seeing them outside doesn't mean your house is in trouble.

But if you're finding them inside, especially in late winter or early spring before it's warm enough for ants to be active outdoors, that's a different story. Carpenter ants don't migrate into a heated house in the cold months from the yard. If they're walking across your kitchen floor in March, it usually means there's a nest already living somewhere inside your walls, and it's been there long enough to get comfortable. The ants you're seeing are coming out, not coming in.

Same goes for winged swarmers. A few flying ants near an outside light? Normal. Winged ants showing up at your living room window, trying to get out? That's a colony that's set up shop inside the structure and is now mature enough to produce a new generation. That doesn't happen overnight. It points to a nest that's likely been active for two or three years.

Why Carpenter Ants Are a Bigger Deal Than Other Ants

Most ants are a nuisance. Carpenter ants are a structural issue.

The name is a bit misleading, because they don't actually eat wood the way termites do. What they do is hollow it out to build their nests, carving smooth tunnels and galleries through it. They go after wood that's already softened by moisture first: around leaky window frames, under bathroom and kitchen subfloors, in damp basement joists, behind that spot on the fascia where the eavestrough's been overflowing for a couple of seasons. Once they're established, they'll branch out into sound, dry wood too.

The damage is slow, but it's real, and because it happens inside the wood where you can't see it, people often don't notice until a colony has been working away for years. A mature nest can hold thousands of ants. Left alone long enough, they weaken the very framing that holds parts of your home up. It isn't as fast as termite damage, but in our part of Ontario, carpenter ants cause far more home damage than termites ever do, simply because they're so much more common here.

There are two clues that tip you off to active tunnelling. The first is frass, a fine pile of what looks like sawdust or wood shavings, sometimes mixed with bits of dead insects, that builds up below where they're nesting. They push this debris out of their tunnels the way wood shavings pile up under a workbench. If you find a small cone of “sawdust” under a window frame or in the basement and you didn't put it there, that's worth a hard look.

The second is sound. In a quiet house at night, a large active nest inside a wall can make a faint, dry rustling or crinkling noise, a bit like cellophane being slowly crushed. People hear it and assume it's the house settling or something in the attic. Sometimes it's carpenter ants.

Why the Can of Spray Doesn't Fix an Ant Infestation

When you spray the ants you can see, you're killing foragers, the workers sent out to find food. They're a tiny fraction of the colony, and they're expendable. The queen, the brood, and the bulk of the nest are tucked deep inside the wood where the spray never reaches. Knock out the visible ants and the colony just sends more. Worse, some over-the-counter sprays can cause a stressed colony to “bud,” to split off and start satellite nests elsewhere in the house. So you can spray and genuinely make the problem bigger.

Getting rid of carpenter ants properly means finding the nest, or nests, since established colonies often have a main nest plus satellites, and treating the colony at the source. That usually means targeted baits the workers carry back to the queen or treating the galleries directly once they're located. It also means dealing with the moisture problem that drew them in, because if you fix the ants but leave the damp wood, you're just setting the table for the next colony. This is genuinely hard to DIY well, which is why it's worth getting a professional carpenter ant control treatment rather than fighting a losing battle with the spray can.

What to Do If You Think You've Got Carpenter Ants

Don't panic, and don't reach for the spray. The single most useful thing you can do is figure out whether you're seeing them inside or outside, and roughly where. If it's the odd ant near the back door in summer, keep an eye on it. If you're finding them indoors, finding frass, or hearing that rustling in the walls, it's time to have an exterminator take a look before the colony gets bigger.

A proper inspection traces where the ants are nesting, which is the whole ballgame, because you can't treat what you haven't found. If you want a straight answer about whether those big black ants are a real problem or just the occasional wanderer, that's exactly the kind of thing a local ant exterminator in Barrie deals with every spring. The treed, older neighbourhoods around here are prime carpenter ant territory, and so are the cottage and lakeside properties, where moisture and mature trees act like a magnet. That's why pest control in Orillia sees plenty of these calls once the weather warms up.

Carpenter ants aren't a reason to lie awake at night. But they are a reason to look a little closer at that big black ant instead of just squashing it. The sooner you know what you're dealing with, the smaller and cheaper the fix tends to be. If you'd rather skip the guesswork entirely, a quick call to your local pest control company or a look through the full range of pest control services on offer will tell you whether it's time to act or just keep watching.