When a rotten smell hangs around one stretch of wall, the first instinct is to find someone to take the animal out. It is also the case where removal is least often possible. Whether there is anything to take away depends on what is in there, and on whether anyone can reach it without cutting through the wall.
What is the smell in the wall likely to be?
Often a mouse. Mice move through the hollow spaces behind drywall, and a mouse that dies in one is shut into a narrow pocket with almost no air moving through it. If it is a mouse, the cleanup advice further down matters: Colorado's health department names the deer mouse as the species most often behind hantavirus infections in the state.
A bat is the other animal to keep in mind. Colorado Parks and Wildlife says the big brown bat can turn up almost anywhere in the state, especially in towns and cities, and that it is more closely associated with humans and development than any other bat in North America.
It may not be an animal at all. A drain trap that has dried out, standing water in an appliance drip pan and damp material can all produce a smell people take for decay. A rotten-egg smell is a different matter: get everyone outside and phone the gas utility from there.
Can it be reached without cutting the wall?
Sometimes, because the animal may not be where the smell suggests, or the spot may be reachable without touching a finished surface. These are the ways in that operators use:
- from the attic, above the top of the wall
- from an unfinished basement or a crawl space, below it
- through an opening that is already there, such as an access panel or an unfinished garage wall
Operators reached through this site do not cut into drywall, plaster, a ceiling or any other finished surface to get at a carcass. If the animal can be reached through one of the routes above, that is a normal removal. If it is sealed inside a finished wall with no way in, there is nothing for an operator to remove, and nobody will be sent to open the wall.
Why not just open the wall?
Opening the wall is often not the first step, for practical and health reasons. Pinpointing the right stretch of wall by smell alone is hard, and cutting, patching and repainting is building work for the owner and a contractor to decide on.
The health side concerns rodents. Colorado's health department says never to vacuum or sweep when cleaning up rodent-infested areas, because doing so may raise the risk of breathing in virus particles. Cutting into a cavity where mice have been nesting would disturb the same kind of droppings and nesting material, which is our reason for not rushing it. If the wall does get opened, the cleanup should follow the CDC steps the department links to:
- open the doors and windows for 30 minutes and leave the space while it airs
- wear rubber or plastic gloves
- spray the dead mouse, any nest and the area around it with disinfectant or a mix of 1.5 cups of household bleach to a gallon of water, and let it soak for 5 minutes or as the label directs
- bag it with any traps, tie the bag, put it in a second bag, and throw it in a covered garbage can
What if it might be a bat?
Then the first call is to your local health department, not to anyone who removes animals. Colorado's health department names bats and skunks as the main sources of rabies in the state and tells people to avoid all contact with bats. Colorado Parks and Wildlife says that if a bat is in your house, or anyone has touched one or might have, you should call the local health department for directions, because it may want the bat tested. Do not throw a bat away before you have spoken to them.
How long will the smell last?
There is no reliable number of days, and none is given here. What follows is a field pattern, not a laboratory figure: the smell of a small rodent generally lessens as the body dries out and decomposition runs its course. How long that takes changes with:
- the size of the animal, since a mouse is far smaller than a squirrel or a rat
- the temperature inside the wall, which an exterior wall or a nearby heat source changes
- moisture and airflow in the cavity
- where exactly it lies, including whether it is against insulation
What can I do while it fades?
Air the room when you can, and keep children and pets away from that stretch of wall. Look in the attic, the basement and the garage for droppings or chewed nesting material, which show where mice have been, and clean any you find the CDC way rather than with a broom or a vacuum. Watch for anything that changes the picture: flies gathering at one window or light fitting, a bat inside the living space, or a smell that spreads through the house rather than staying in one place.
When is a call worth making?
When the smell leads somewhere that can be reached. If it is strongest at the attic hatch, the crawl space door, a garage wall or a deck, the animal may be in a space an operator can get into, and that is worth describing on a call. Where an operator covers the address, the visit and the price are agreed on the call. If everything points to an animal sealed inside a finished wall, the answer is the one above: no operator will remove it, and the smell generally lessens as it dries out.
General information for Colorado homeowners, not medical or legal advice. Rabies and hantavirus questions belong with your local health department or your doctor.