What you’re smelling
An animal died inside your structure — most often in a wall cavity, above a ceiling, under a floor, in a duct, or in the crawl space. The smell is not a plumbing problem and it is not mould. Once you have ruled out a dry drain trap, decomposition is a distinctive, sweet-rotten odour that gets worse when the house is closed up and warm.
The useful mental model: this is a located problem, not a treated problem. Nothing you spray will help. The entire job is finding it and getting it out.
Let the flies do the work
Blowflies find a carcass within a day or two, far faster than you will. They lay eggs on it, and the adults congregate at whatever gap is closest to the source — a light fixture, an outlet, a gap where trim meets drywall, a ceiling seam.
If you have a cluster of flies at one spot on a wall or ceiling, that is the strongest signal you will get. Combine it with the nose test at different heights along the wall and, after a few days, a yellow-brown seepage stain. Where flies, smell, and stain converge, cut there.
If flies appear at an interior wall with no plumbing in it, that is a wall cavity carcass almost by definition.
Once you’ve located it, the location picks the trade
Same principle as a ceiling stain: you don’t route by how bad the smell is, you route by where it’s coming from. Go to the strongest point and work out what you’re standing next to.
Inside a wall, ceiling, or floor cavity → wildlife / dead animal removal company. This is the default case, it needs a cut, and it is the one general pest control will decline.
Worst at the supply vents and it intensifies when the system runs → HVAC technician, not a wildlife company. Something died in a duct run or in the air handler cabinet. They have the access panels and the duct camera; a wildlife company has neither and will cut your wall looking for something that isn’t there.
Crawl space, or strongest at floor level in the lowest room → wildlife / dead animal removal, but ask about crawl space access before booking. Expect a surcharge, and expect the vapour barrier and under-floor insulation to be part of the quote — soaked material holds the smell long after the carcass is out.
Attic, or strongest upstairs and on hot afternoons → wildlife removal, usually with no cutting required. Attic carcasses are often simply reachable, which makes this the cheapest version of the job. Get the insulation checked in the same visit.
Chimney or fireplace → wildlife removal or a chimney professional. Birds and squirrels drop down uncapped flues routinely. Cap it afterwards, not before.
Under a deck, porch, shed, or the exterior of the house → wildlife removal, and a cheaper job than anything inside. No structure has to be opened.
Lying in the open in your yard or garage → you, honestly. Gloves, a shovel, two bags, and your household bin if local rules allow. A call-out for a squirrel on the lawn is money you don’t need to spend.
On the road, the verge, or public land → city animal control or public works, and usually free. This is the one dead-animal call animal control genuinely takes, and it’s the mirror image of the raccoon-in-the-attic situation where they’ll turn you down.
Under or behind a major appliance — fridge, dishwasher, washing machine → you or an appliance technician. Pull the unit out before you call anyone about walls.
In a vehicle → a mechanic or an auto detailer. Cabin air filter housing and blower motor first.
Smell but no flies, no stain, and nothing found → not a carcass. Run every tap and flush every toilet to refill dry P-traps, then think about the sewer vent or a gas appliance. That is a plumber or, if you smell gas at all, the gas utility.
Why the smell peaks and then fades
Decomposition is a curve, not a plateau. Odour builds through the bloat stage, peaks over roughly the first one to two weeks for a small animal, then declines as the remains dry out. This matters for two reasons.
First, it means “it’s getting worse” is not evidence that something new has happened. It’s the expected shape.
Second, it means waiting is a real option for a mouse — a few days to two weeks, and it’s over. For anything the size of a rat, squirrel, possum, or raccoon, waiting means weeks of a genuinely unliveable room, plus flies emerging into the house, plus a grease stain in the drywall you will end up cutting out anyway.
Who cuts the wall open
A wildlife removal company is the right call. They will locate, cut the smallest sensible access hole, bag the remains, treat the cavity with an enzymatic cleaner, and often deodorise. Ask two questions before hiring:
- Do you patch the drywall, or do I need my own contractor? Many do not patch. Budget for a handyman afterwards.
- Is cleanup and deodorising included, or is that separate? This is where quotes diverge most.
A general pest control company may or may not offer this. Standard quarterly contracts almost always exclude it.
If the smell is worst from the supply vents and intensifies when the HVAC runs, call an HVAC technician instead — a rodent in a duct or dead in the air handler is their access, not a wall cut.
Expect to be turned down at least once
This is the category where people spend two days being politely declined, so it’s worth knowing in advance who says no.
- Pest control is the most common refusal, and the most surprising one to homeowners: “Pest control said no.” Their licence and their contract are built around live insects and rodents. Carcass retrieval, crawl space entry, and cutting drywall are usually all outside it. Some companies do offer dead animal removal as a separate service — ask for it by that name rather than assuming.
- Municipal animal control will collect a dead animal from a public road and decline the identical animal inside your wall. Public land yes, private structure no.
- Plumbers will decline unless you have actually established it’s a drain or vent problem. They’re a reasonable call only after the dry P-trap test fails.
- Drywall contractors and handymen will patch after removal but will not go looking for the source, and shouldn’t.
- Restoration and biohazard companies will take the cleanup and often the removal, but many won’t do the locating — they want you to know where it is.
- Insulation contractors will decline to work in a contaminated attic or crawl space until it has been remediated.
Search terms that actually reach someone: dead animal removal, nuisance wildlife control operator, wildlife removal, animal damage control, biohazard remediation. “Exterminator” mostly reaches the trade that will say no.
The order to do this in
- Rule out the free explanations first — every drain run, every toilet flushed, and a sniff test outside near the air intake. A dry P-trap costs nothing and is the most common false alarm on this page.
- Confirm dead, not alive. If you still hear scratching or scrabbling anywhere in the structure, you have a live-animal job as well, and it goes first. Cutting or sealing on the assumption that everything in there is dead is how people release a panicked raccoon into a bedroom.
- Locate before anyone cuts. Flies, nose, stain. A technician who arrives to an unlocated smell either charges for the search or guesses, and both are worse than an evening of your own time.
- Remove, then clean. The carcass is the small half; contaminated insulation and residue is the rest.
- Seal the entry. Same visit if you can.
- Patch last. Never let anyone close a hole until removal is confirmed. A patched wall over a missed carcass is a second wall to open.
The expensive reversal is patching or sealing before removal is confirmed. The slow one is deodorising first, which masks the only signal you were navigating by and adds days to the search.
Insulation and contamination
If the animal was living in your attic before it died, the carcass is the small half of the problem. Soaked insulation, accumulated droppings, and urine staining are the rest. Fixr prices professional biohazard cleaning of rodent contamination — removing feces and urine, deodorizing, disinfecting, plus a biohazard fee — at $200 to $550.
Handle any of it yourself and the rules are simple: gloves, an N95, no dry sweeping, no vacuuming without a HEPA unit. Mist the material with disinfectant before you disturb it.
Then find out how it got in
An animal that died in your wall got into your wall. If nobody seals the entry, you will be reading this page again in a year. Ask the removal company to inspect the roofline, soffits, vents, and foundation gaps while they are there, and get the exclusion work quoted at the same time — it is far cheaper as one visit than two.