Wasp Nest Inside Your Wall? Why September Is When You Hear It

Quick answer: A steady buzzing or dry rustling inside a wall in late summer is usually a yellowjacket colony nesting in the wall void. Do not spray the entry hole, and do not seal it. Both push a colony of several thousand insects to chew its way toward the only other opening it can find — which is frequently the inside of your house. Wall-void removal means treating the void itself through the correct access point, then confirming the colony is dead before anything gets closed up. Sani IQ removes wasp nests at $247 per nest at standard access, and every service begins with a $95 inspection, credited when you book the treatment. Call (705) 302-1887.

There is a specific phone call we take every September. Somebody is sitting in a quiet room — often a bedroom, often at night — and can hear something inside the wall. Not scurrying, not scratching in bursts the way a mouse does. A low, continuous, papery hum that gets louder in the afternoon and quieter after dark.

That is the sound of a mature wasp colony, and September is when it peaks.

What you are actually hearing

Yellowjacket and hornet colonies follow a hard annual curve. A single overwintered queen starts a nest in May with a handful of cells. Through June and July the workers she raises take over the building. By late August and early September the colony hits maximum population — several thousand workers, with a nest inside a wall cavity that may be the size of a basketball or larger. That is why you notice it now and did not in June: two hundred wasps in a wall void are silent through drywall, and three thousand are not.

Two things tell you it is wasps and not rodents. The hum is continuous and pitch-stable, not intermittent. And it tracks the sun — loudest in the warm afternoon when foraging traffic is heaviest, quieter at night and on cold mornings. Mice do the opposite: quiet by day, active after dark, scratching rather than humming. You may also see a faint stain bleeding through drywall or ceiling paint, which is nest moisture and larval waste. In Markham and across York Region, most of these calls turn out to be yellowjackets that came in through a gap in the siding or a soffit joint.

How they got in

Wasps do not chew their way into a wall. They find an existing gap, usually one you would never notice from the ground:

• Where siding meets trim, or an unsealed J-channel
• A soffit or fascia joint that has separated
• The gap around a dryer, bathroom or range vent
• An unsealed utility penetration — cable, gas line, hose bib, AC line set
• A weep hole in brick veneer, or a gap behind a shutter
• A window or door frame where caulking has failed

Once inside, the colony builds in the cavity between exterior sheathing and drywall, or in the soffit, attic edge or box header. From outside, all you see is a small opening with steady two-way traffic. From inside, you hear it.

This is why wall-void nests turn up on well-maintained houses too. It takes a 6 mm gap. Homes across Vaughan built in the last twenty years get them as reliably as century homes do — the entry points are just in different places.

The three mistakes that turn a wall nest into a drywall repair

Almost everything that goes badly wrong with a wall-void nest comes from one of these three.

Mistake 1: spraying the entry hole

This is the classic, and the one that does real damage. Hardware-store aerosol is engineered to knock down an exposed aerial nest at range; it cannot reach a nest sitting half a metre back inside a cavity. What it does instead is kill the foragers at the entrance, saturate the opening with an irritant, and alarm the colony.

Several thousand wasps that suddenly cannot use their front door do not give up — they look for another exit. Yellowjackets chew; that is how they make nest material in the first place, and drywall is considerably softer than the wood and siding they normally work with. The wasps that come through into a bedroom are wasps you personally redirected.

The other version of this mistake is spraying at dusk, seeing no activity next morning, and assuming success. You killed a few hundred foragers. The queen, the brood and the bulk of the workers are untouched, and traffic rebuilds within days.

Mistake 2: sealing the entry hole

Foam, caulk, steel wool, tape — the instinct is understandable and exactly backwards. Sealing a live colony’s only exit produces the same outcome as spraying it, just more reliably: several thousand insects with no way out, chewing toward the nearest light and air. That is your interior. Never seal a wall-void entry until the colony is confirmed dead. Sealing is the last step of the job, not the first.

Mistake 3: waiting for frost

This one sounds sensible. Ontario winter does kill wasp colonies: workers die off with sustained cold, mated new queens disperse to overwinter elsewhere, and the colony does not survive to spring. So why not wait?

Two reasons. First, the timeline is worse than people expect: six to eight more weeks of an active, maximum-size colony in your wall — and September and October wasps are the most defensive of the year. The food supply collapses, the colony stops raising brood, and workers become erratic and far quicker to sting. That is a long time to live beside a bedroom wall.

Second, “they died off” is not the same as “the nest is gone.” The dead nest stays in the cavity — paper, dead brood and larval waste — and over winter it draws a secondary problem: carpet beetles, larder beetles, sometimes mice, all working through the protein left behind. Homeowners who wait out the wasps often call in February about small beetles in an upstairs room and have no idea the two are connected. The moisture and staining can also bleed through finished surfaces.

Wasps do not reuse last year’s nest, but new queens reliably pick the same structural gaps, because those gaps are attractive for the same reasons they were last May. An untreated, unsealed entry point is a standing invitation.

How the removal is actually done

Wall-void work is genuinely different from removing a nest off a soffit or a tree branch, and it is the reason this is not a DIY job.

A technician first confirms the nest’s actual location and extent, which is not always where the entry hole is — wasps commonly travel some distance inside a cavity before building. The void is then treated at the right access point with a delivery method that reaches the nest rather than the doorway: typically an injected dust that workers carry through the colony, not an aerosol that stops at the entrance.

The entry point is left open deliberately, because returning foragers need to come back and pick up the material. Sealing happens on a follow-up, once activity has ceased — and that exclusion step is what stops a new queen from choosing the same gap next May.

A disturbed mature colony in a confined space is the single most likely stinging scenario a homeowner meets in an Ontario year. Health Canada’s guidance on wasps is blunt about leaving large or hard-to-reach nests to a licensed professional, and a wall void is the textbook version of hard-to-reach.

To identify what you have before you call, our yellowjacket identification page covers the species behind most wall-void nests in Ontario, and our paper wasp guide covers the one you are more likely to find under a deck or eave.

What it costs, and what actually keeps it from happening again

Wasp and nest removal is $247 per nest at standard access. If your nest needs extension-ladder or roof access, that is quoted before any work starts — you will know the number before we begin, not after. Every service starts with a $95 professional inspection, credited in full when you book the treatment, and one-time services carry a 60-day guarantee.

That is the entry point. Here is the part worth two minutes of thought.

A wall-void nest is not really a wasp problem. It is a building-envelope problem that wasps found. The gap in the siding, the separated soffit joint, the unsealed vent penetration — those were there before the queen arrived in May, and unless someone addresses them they will still be there next May. Roughly the same gaps are the ones mice use in October. Removing the nest solves this year; it does not solve the reason it happened.

That is what our annual plans are built around. General Insect Control is $845 a year and Essentials is $1,195 — scheduled visits through the season, exterior treatment before colonies establish rather than after they are three thousand strong, and attention to the entry points that keep letting things in. A queen intercepted in May is a nest that never gets built. A nest caught in June is the size of a golf ball on an exposed eave, not a basketball inside your wall.

The economics are not subtle: one wall-void removal plus drywall repair, staining, and the beetle problem that follows an untreated dead nest runs past a year of protection quickly — before you count six weeks of not being able to use a bedroom.

The fastest way to find out what your situation needs is our free quote quiz. Or call (705) 302-1887 and describe what you are hearing; we can usually tell you over the phone whether it is wasps or rodents.

Sani IQ is licensed under the Ontario Pesticides Act, registered with the MECP, BBB Accredited, carries $5M liability coverage, and holds a 5.0 Google rating. We serve the GTA, York and Durham Regions, Simcoe County, Barrie, Orillia and Muskoka, and in Richmond Hill we handle wall-void nests regularly through September and October. Our technicians are employed, licensed and background-checked — never subcontracted.

Frequently asked questions

How do I know it is wasps and not mice in my wall? Wasps produce a continuous hum, loudest in warm afternoon hours and quiet at night. Mice produce intermittent scratching and gnawing, loudest after dark. If the sound follows the sun, it is wasps.

Can I just plug the hole at night when they are all inside? No. That is the single most reliable way to force a colony through your drywall. Never seal a live nest’s entry.

Does the nest have to come out of the wall? Usually not. Nest material is normally left in place once the colony is dead, because opening the wall causes more damage than the remaining paper does. Where a nest is very large or already staining through, removal through an access cut is the better call.

How long until they are gone after treatment? Activity drops sharply within 24 to 48 hours and stops within a few days as returning foragers carry the material through. We confirm activity has ceased before anything gets sealed.