Carpenter Ant Control in Toronto: How to Spot Them, Why They Show Up, and How We Get Rid of Them

If you've found large black ants marching across your kitchen counter, or a few winged ones near a windowsill, there's a good chance you're dealing with carpenter ants. They're one of the most common calls we get across Toronto and the GTA, especially from late spring through summer.

Carpenter ants aren't just a nuisance. Left alone, they tunnel through the wood in your home to build their nests, and over a few years that can actually weaken the structure. The good news is they're very treatable once you know what you're working with. Here's the full picture.

What carpenter ants actually look like

Carpenter ants are big. The black carpenter ant is the most common species in Ontario, and workers run anywhere from about 6 to 13 mm long. If you put one next to a ruler like in the photo above, you'll see they're noticeably larger than the little ants you find on a sidewalk.

A few things to look for:

• Color: mostly black, sometimes dark red and black.
• Size: large, and you'll often see different sizes from the same colony.
• Shape: a single rounded "hump" on the back and a smooth, evenly curved thorax.
• Wings (on some): the reproductive ants have wings, with the front pair longer than the back pair.

That last point matters more than people realize, which brings us to the photo at the top of this post.

Found flying ants inside? Here's what that really means

The ants in the cover image are winged carpenter ants, also called swarmers. These are the reproductive males and females a colony produces once it's mature. They fly out to mate and start new colonies.

Here's the part most homeowners don't know. If you're seeing swarmers inside your house, it almost always means there's an established nest already living in your walls, not ants that wandered in from the yard. Carpenter ant colonies don't produce swarmers until they're roughly 3 to 5 years old and have thousands of workers. So winged ants showing up indoors in spring or early summer is a pretty reliable sign the colony has been there a while.

People often vacuum up the flying ants, feel relieved, and assume the problem's gone. It isn't. You killed a handful of reproductives. The nest, and the thousands of workers chewing through wood, is still in there. If you've seen winged ants indoors, that's the moment to call a pro, not wait it out.

Why carpenter ants come into your home in the first place

Carpenter ants want two things: shelter and moisture. Understanding that explains almost everything about where they show up.

In nature, carpenter ants nest in dead trees, stumps, and damp logs. Your home just looks like a giant version of that to them, especially anywhere the wood is soft, damp, or already starting to rot. They don't eat the wood (more on that below), but they love to tunnel into wood that's easy to dig through, and moisture is what softens it up.

That's why we almost always find them in the same spots:

• Under and around kitchen sinks
• Behind dishwashers and bathroom vanities
• Around windowsills and door frames
• In bathroom walls near showers and tubs
• In attics, basements, and around any past water damage

In the GTA, a few things make it worse. Older Toronto housing stock often has small leaks or aging window seals that keep wood damp. Our freeze-thaw winters and humid summers are hard on caulking and flashing, which lets moisture creep in. And a lot of homes have mature trees right up against the house, so a colony living in a backyard stump or fence post is one short trip away from moving indoors through a branch, a wire, or a foundation gap.

So when people ask "why me," it's usually some mix of moisture they didn't know about plus an easy way in.

Do carpenter ants actually damage your house?

Yes, but not the way people assume. This is the single biggest point of confusion, so it's worth being clear.

Carpenter ants do not eat wood. Termites eat wood. Carpenter ants excavate it. They chew through the wood to hollow out smooth tunnels (called galleries) for their nest, and they push the debris out. That debris is the giveaway.

If you find small piles of what looks like sawdust, often mixed with bits of insulation or dead insect parts, that's called frass, and it's basically the ants taking out the trash. Find frass and you've usually found a nest nearby. You might also hear a faint rustling inside a wall if the colony is large and active.

On its own, one season won't collapse your house. But carpenter ant nests grow, and they often build satellite nests through a structure over time. Years of tunnelling through joists, studs, and window framing genuinely weakens wood. That's why catching it early is so much cheaper than catching it late.

How we treat carpenter ants at Sterex

Here's where a professional treatment is different from anything you can buy off a shelf. Killing the ants you see does nothing. The goal is to wipe out the colony, including the queen and the workers hidden in the walls. That takes the right products in the right places.

Our carpenter ant treatment focuses on the spots they actually live and travel:

• Windowsills and door frames get sprayed, since these are major travel routes and common nesting zones.
• Under sinks and around plumbing get treated directly, because that's where the moisture is and that's where we find them most.
• Exterior entry points and trails around the foundation get treated to cut off the path between an outdoor colony and your home.

We use professional residual products like Dragnet and Seclira, which keep working for weeks after we apply them. For tougher, hidden nests, we'll use a method called Actisol, where we inject treatment into voids and tight spaces (for example fumigating under a sink cabinet) to reach a nest you can't get to with a normal spray.

One thing we always tell clients up front: this doesn't work overnight. A residual product isn't a contact killer. The way it works is the ants walk through the treated zones, carry it back into the nest, and spread it through the colony. Over the next couple of weeks you'll see the population drop off as that works through the nest. Seeing a few ants in the days right after treatment is normal and actually a good sign that they're moving through the product. Give it time.

Why store-bought sprays usually don't fix it

We get it. Before calling anyone, most people try the sprays from Home Depot or Canadian Tire first. There's nothing wrong with trying, but it helps to know what those products actually do.

Most off-the-shelf sprays are contact killers. They kill the ant in front of you and that's it. The colony in your wall never gets touched, so the ants just keep coming. Baits can work better because the ants carry them back to the nest, but they're slow, they require the ants to actually take the bait, and against a large established carpenter ant colony they often don't go far enough.

So if you've put out bait, sprayed the baseboards, and you're still seeing ants weeks later, that's your sign. It's not that you did it wrong. It's that the problem is bigger than what those products are built for, and at that point it's worth bringing in a professional before the nest grows and the wood damage adds up.

When to call us

Call sooner rather than later if you're seeing any of these:

• Winged ants inside the house (the big one, it means an indoor nest)
• Large black ants showing up regularly, especially in the kitchen or bathroom
• Small piles of sawdust-like frass near baseboards, windows, or under sinks
• A faint rustling sound inside a wall
• Ants that keep coming back no matter what you spray

We treat carpenter ants across Toronto, Brampton, Mississauga, and the rest of the GTA. If you want it dealt with properly, call us at 289-210-7378 for a quote and we'll sort out a plan for your home.