Dead Rodent Smell: How to Find It and Get Rid of It

Why it happens

The most common cause is bait. A rodent that eats poison goes back to a hiding spot and dies there, often inside a wall, under attic insulation or in a crawl space. University of California guidance recommends sealing entry points before baiting outdoors so poisoned rodents do not die inside.

Other causes include traps that were set and forgotten, rodents trapped in a space that got sealed, and rodents that got into ducts or appliances.

How long the smell lasts

It depends on the size of the animal, the temperature and the airflow. A mouse may smell for days. A rat in a warm attic or a closed wall can smell for several weeks. Memphis summers speed up decay, so the smell gets strong fast and may fade sooner, but it is miserable while it lasts.

Waiting it out is an option only if the source truly cannot be reached. Removal is faster.

How to find the source

Follow the smell. It is usually strongest close to the carcass, though it can travel through ducts and wall cavities. Clues:

• Flies gathering at a wall, light fixture, window or vent
• A stain on the ceiling or wall
• The smell is worst near a floor register or return vent
• One closet or cabinet smells more than the rest

Check the attic above the smell, the crawl space below, behind appliances and under cabinets. In older Memphis homes with balloon framing, the carcass can be some distance from where the smell seems strongest.

Removing it safely

The CDC's steps for dead rodents:

1. Wear rubber, latex or vinyl gloves.
2. Spray the rodent, nest and area with disinfectant or a bleach solution and let it soak for 5 minutes.
3. Put the rodent and any nest material in a plastic bag and seal it.
4. Put that bag inside a second bag and seal it.
5. Put it in a covered trash can that is emptied regularly.
6. Disinfect the area, then disinfect and remove your gloves and wash your hands.

The CDC also notes fleas are common on rodents and suggests a DEET repellent on clothing, shoes and hands.

When the wall has to be opened

If the carcass is inside a finished wall or ceiling and cannot be reached from the attic, crawl space or an appliance opening, a small access hole may be needed. A technician can usually narrow the spot first so the hole is small. Ask before work starts whether patching is included or whether you will need a drywall repair. See dead rodent removal.

Getting rid of the lingering odor

Once the carcass is out, clean and disinfect the spot. Remove soiled insulation or nesting material. Ventilate the area. Enzyme-based odor products made for organic odors can help on surfaces. Avoid spraying air freshener into walls or ducts; it masks the problem without fixing it.

If a duct was involved, have the HVAC system checked. A torn or chewed duct can keep pulling attic or crawl space air into the house.

Dead rodents in ducts and appliances

If the smell is strongest when the heat or AC runs, the rodent may be in or near ductwork. In Memphis homes, ducts often run through attics and crawl spaces, where rodents can get into torn flexible duct. Turn the system off and have a technician or HVAC contractor check before running it again.

Appliances are another hiding spot. Mice die behind and under refrigerators, dishwashers and stoves, and inside the base of the dishwasher. Pull the appliance out carefully and check with a flashlight.

Cars are a third spot. A rodent that dies in an engine bay or the cabin air intake makes the car smell every time the fan runs. Check under the hood and replace the cabin air filter if needed. See rats in car engines and garages.

Stopping it from happening again

If bait caused it, switch to traps inside the house. If rodents are still getting in, find and seal the openings. If more rodents may have eaten bait, expect more odors over the next week or two. See why rats come back and rodent exclusion, or call to reach a local technician.