Wasp Nest Inside a Wall or Soffit: Why August Is When You Finally Hear Them

Quick answer

If you’re hearing a faint scratching or rustling inside a wall or soffit in August, and you’re seeing wasps coming and going from one small spot outside, you have a nest in a void — not on the surface. Do not spray the entry hole and do not seal it. Both push the colony deeper into the wall and often into the living space. Mark the entry, keep people and pets away from that side of the house, and have it treated from the outside by someone who can do it without opening the wall. Sani IQ handles in-wall and soffit nests across the GTA and York Region — (705) 302-1887.

Why you’re only hearing it now

A wasp colony that’s been inside your wall since May was silent for a reason: in June it held maybe thirty workers. By mid-August the same nest can hold several hundred to a few thousand, depending on species. That’s when three things happen at once.

The nest gets large enough to make contact with the drywall or soffit panel, so chewing, wing movement and workers crossing paper comb finally transmit into the room. Traffic at the entry hole goes from occasional to constant. And the colony switches diet — earlier, workers hunt protein for larvae; in late summer the queen stops laying and the workers shift to sugar. That’s why they seem to be everywhere around your barbecue and recycling at exactly the moment the nest is loudest.

So the timing isn’t a coincidence and it isn’t a new nest. Mid-August is when a nest you’ve had for three months announces itself — at the point of maximum defensiveness, which is what makes the wrong response expensive.

How to tell it’s inside a void, not just on the wall

An exposed nest — the grey paper football under an eave, or the open umbrella-shaped comb under a deck rail — is a visible object. A void nest isn’t. You’re diagnosing it from indirect signs:

• A single, consistent entry point. Watch the exterior for two or three minutes. If wasps are funnelling in and out of one specific gap — a soffit seam, a brick weep hole, a gap where the siding meets the fascia, a vent louvre, a crack around a window frame — the nest is behind it.
• Sound with no visible nest. Faint rustling, a papery crackle, or something people often describe as a distant sizzle. Usually loudest in the afternoon and quiet after dark.
• A staining or damp patch on drywall or ceiling. Large nests generate moisture and, in extreme cases, the comb can bleed through a ceiling. This means the nest is big and it’s a call-today situation.
• Wasps appearing inside the house one or two at a time, especially near a ceiling light fixture, a pot light, or a bathroom exhaust fan. That means the nest has found a path through the vapour barrier.

The GTA housing details that make this common

In older Toronto and Etobicoke brick homes, the usual route is a brick weep hole — the small vertical gaps left in the mortar joints above windows and near grade to let the wall cavity drain. They’re supposed to be there. They’re also perfectly sized for a founding queen in April, and they open directly into the air gap behind the brick veneer. Once the colony is in that cavity, it’s between the brick and the sheathing, and there’s no way to get to it from inside without removing brick.

In newer Vaughan and Markham subdivision builds, the more common route is the soffit. Aluminum soffit panels are clipped into a channel, and a panel that has popped a clip or pulled at a corner — often from ice damming or a bad fascia install — leaves a slot into the roof overhang. Yellowjackets in particular will build in that overhang and, if the attic baffle isn’t sealed, expand into the attic itself.

Other repeat offenders across the GTA: gaps where a deck ledger board meets the house, vent hoods with a broken flapper, the void under a bay window, and hollow porch columns.

The three things that make it worse

1. Spraying the entry hole. This is the big one. A can of aerosol wasp spray fired into a void nest does not reach the comb — it hits the first few centimetres and the workers behind it. What it does reliably do is alarm the colony. Alarmed wasps in a wall move away from the disturbance, which means deeper into the cavity, along the joist bays, and toward the path of least resistance. In a lot of houses that path is the interior. We have taken calls from homeowners who had two wasps a day in the kitchen before they sprayed and forty in the bedroom afterwards.

2. Sealing the entry hole. Same mechanism, worse outcome. Caulking or foaming the entry with a live colony behind it doesn’t trap the wasps — it makes them chew a new exit. Paper wasps and yellowjackets will chew drywall. The new exit is very often into the room. Sealing is the last step of the job, done after the colony is confirmed dead, and it should always be done.

3. Opening the wall. Cutting drywall to “see what’s in there” puts you in a confined space with a defensive colony at peak population and no exit route. Don’t.

If you want the full picture on the DIY-versus-professional calculation for wasps generally, we’ve written it out here: Can you remove a wasp nest yourself?

Yellowjackets or paper wasps — it changes the job

The two most common void-nesters in Ontario behave differently enough that identification matters before anyone touches anything.

Yellowjackets are the aggressive ones. They build fully enclosed paper nests inside cavities — wall voids, soffits, attics, and underground — and a mature late-summer colony can run into the thousands. They defend the nest at distance, they can sting repeatedly, and they’re the species behind most late-August emergency calls. They’re also the ones at your patio table in September. Identification and behaviour: yellowjackets.

Paper wasps are the slimmer, longer-legged wasps that build the open, downward-facing umbrella comb. They’re far less aggressive and their colonies are smaller — dozens, not thousands. They usually build in semi-sheltered spots rather than deep voids, but they will use a soffit or a porch ceiling. If what you have is paper wasps in an accessible overhang, the job is much smaller. Details: paper wasps.

A third possibility in a wall or soffit is bald-faced hornets, which are actually a yellowjacket relative and are treated the same way — as a serious, keep-your-distance job. Our full identification guide covers all of them: Wasps and hornets in Ontario: the complete field guide.

What to do right now, before anyone arrives

• Mark the entry point with a piece of tape a foot or two away from it — not on it. You want to be able to point at it, and a technician working at dusk will thank you.
• Close the windows on that side of the house, and check the screens.
• Keep that side of the yard clear. Kids, pets, patio furniture, the barbecue. Yellowjackets defend a radius, and lawnmowers and string trimmers near a ground or low-wall nest are a classic sting event.
• Don’t block the hole. Don’t spray it. Don’t bang on the wall.
• If anyone in the household has a known sting allergy, treat this as urgent and make sure an epinephrine auto-injector is on hand and in date.
• Note when the traffic is heaviest. It helps confirm the species and the size of the colony.

How the job is actually done

Void nests are treated from the outside, through the entry point, at low light — early morning or dusk, when the foragers are home. That matters: treating mid-afternoon leaves a few hundred workers out in the field who come back to a treated nest and mill around the exterior for hours.

The technician applies an insecticidal dust rather than a liquid, because dust travels through the cavity on the wasps themselves. Workers carry it inward across the comb and into contact with the queen and brood, which is what actually kills the colony rather than just the visible traffic. The nest usually goes quiet within a day or two, though you may see straggler activity for a few days after as returning foragers arrive.

Then — and only then — the entry point gets sealed so the same cavity doesn’t get colonised next spring, since a good void is a good void every year. Where the nest is accessible, the comb is removed; where it’s inside a sealed brick cavity, it’s generally left in place, and that’s normal. An abandoned paper nest doesn’t attract anything and degrades on its own.

For a walkthrough of what a standard removal looks like start to finish, see What happens during professional wasp nest removal.

Where we work

Sani IQ handles wasp and hornet work across Toronto, Vaughan, Markham and the wider GTA, with dedicated crews for wasp nest removal in Mississauga, Etobicoke and Toronto, plus York Region, Durham, Simcoe County and up into Muskoka.

Not sure whether what you’re describing needs a technician? Our free quote quiz takes about twenty seconds. If you’d rather talk to someone: (705) 302-1887.

Frequently asked questions

How long can a wasp nest be in my wall before I notice it? Typically three to four months. A queen founds the nest in April or May, and the colony is usually too small and too quiet to detect until it reaches a few hundred workers in late July or August. Hearing it now doesn’t mean it started now.

Will the nest die off on its own in the fall? The colony does — Ontario yellowjacket and paper wasp colonies collapse with the first hard frosts, and only new queens overwinter, elsewhere. But waiting means six to eight more weeks of an active colony at peak size, and the entry point stays open for next spring’s queen.

Can I wait until winter and just seal the hole then? Sealing in late fall is worth doing. The problem with using it as your only plan is the intervening two months of peak activity, plus the risk the colony has already found a way into your living space.

Why do I keep finding single wasps inside the house? The nest has a path through the interior side of the wall — usually a light fixture, a pot light housing, an exhaust fan or a gap in the vapour barrier. A strong sign the nest is large and worth escalating.

Is a soffit nest the same job as one in a wall? Similar approach, different access. A soffit nest can often be reached at the panel seam, though attic spread is the thing to check for. A brick-cavity nest is more constrained and relies on dust travelling through the void.

What if I’ve already sprayed it? Say so when you call. A disturbed colony may have relocated within the cavity or opened a secondary exit, and the technician will want to check the interior as well.