Mice

How to get rid of mice

How to get rid of mice in an Auckland house: confirm it is mice, trap where they run, seal the 6 mm gaps, and the 5 day mouse rule tested against the evidence.

The short answer

To get rid of mice, confirm from the droppings that it is mice, then set plenty of snap traps against the walls where they run, no more than about three metres apart, and check them daily. Mice stay close to the nest, so several traps close together beat one in the middle of the kitchen. Then close every gap of 6 mm or more. If they keep coming, our rodent control covers the whole house.

First, make sure it is mice and not a rat

Mouse droppings are about 3 to 6 mm long, thin, dark and pointed, and scattered along shelves, drawers and the backs of cupboards, while rat droppings are 12 mm or more and grouped. Mice also leave small, scratchy gnaw marks, about 2 mm wide against a rat's 4 mm, nests of shredded paper or insulation and, in a long-standing case, a musky smell.

Timing helps as well. House mice come indoors in autumn, as the nights turn colder, and they are mostly active at night, so a first scatter of droppings in the pantry as autumn sets in is the usual start. Mice are also the rodent people most often deal with themselves, and when the attempt stalls the reason is nearly always where the traps were put or a gap left open, not the product.

If the droppings are bigger, or the noise is heavier and in the ceiling, read how to tell you have rats in the house instead, because rats need a different plan.

The fastest way to get rid of mice

Lots of snap traps, all set on the same day, in the right places. Mice seldom go more than about 9 m from their nest and their food, so traps go every 3 m or so along the walls where the droppings are, in pairs a few centimetres apart, each with a pea-sized dab of bait on the trigger. Check them every morning; in our experience most of a small population is caught in the first week.

One trap fails because a mouse's world is small, and a trap three rooms from the nest may never be visited. Keep the bait small, because a mouse can lick a large blob clean without setting the trap off, and use what they are already eating, peanut butter, or a wisp of cotton wool, which a nesting female will try to carry away. On the same night take away the competing food: everything into sealed containers, nothing left on the bench, and the pet's bowl put away. Do not use glue boards, which cannot be sold or used against rodents in New Zealand without Ministerial approval.

Clean as you go, without sweeping. Wear gloves, spray the droppings with disinfectant and leave it for a few minutes, then wipe them up with paper towels, because sweeping or vacuuming lifts the dust into the air you are breathing. Which trap type suits which room, and when bait is worth using at all, is covered in rat and mouse traps or bait.

Mice in the walls, and what to do when you hear them

A mouse scratching in a wall is usually nesting in the cavity near warmth and food, often beside the kitchen, behind the oven or the dishwasher or near the hot water cylinder, and coming out at night through a gap under the bench or round a pipe. Do not seal that gap while it is in use; trap where the mouse comes out, then seal once the noise has stopped.

Mice do not need to drink, since they get enough moisture from their food, so a wall cavity with a kitchen beside it can keep them going indefinitely, which is the honest answer to how long a mouse can survive in a wall. Find the way out by looking for droppings along the skirting and around the pipes under the sink, and set the traps there, against the wall, rather than drilling holes to put bait inside the cavity.

Mice gnaw wiring as well as food, and a chewed cable inside a wall is a fire risk, so if you find gnawed cable sheathing anywhere, turn that circuit off and call an electrician. A mouse that dies inside a wall leaves a smell you cannot reach, which is one more reason we trap mice in a house rather than bait them.

What is the 5 day mouse rule?

The 5 day mouse rule is an internet rule of thumb rather than any official guideline: keep trapping until you have gone five days in a row with no mouse caught and no fresh droppings or gnawing, and then treat the problem as over. It is a reasonable test, but the US Centers for Disease Control and Prevention sets a stricter one, a full week with no catches and no new signs of rodents.

The count only means something if the traps are still set, baited and in the right places, because a trap that has been knocked sideways or licked clean will happily go five days without a catch while the mice carry on around it. A mouse that has learned to avoid one spot, or a new one coming in through a gap you have not closed, starts the clock again.

How we would use it: clean up all the old droppings at the start, so that anything fresh is obvious; check the traps every morning; and start counting only from the last catch. When you reach a clear week rather than five days, close the gaps and leave one or two traps set where the runs were, as an early warning.

Is it safe to sleep in a house with mice?

In the short term, yes for most people, and a mouse is very unlikely to bother someone who is asleep: mice are nocturnal foragers that keep away from people and go where the food is, which is the kitchen rather than the bedroom. The real issue is contamination, because mice leave urine and droppings as they move, over food and benches, and mouse urine is a recognised allergen linked to asthma in sensitive children.

What to do tonight is simple: food into sealed containers, nothing left out on the benches, no food kept in bedrooms, and a wipe of every surface before you cook on it. University of California guidance lists leptospirosis and salmonella among the diseases mice carry, so if anyone becomes unwell after cleaning up droppings, tell the doctor about the exposure. A baby in the house, or someone with asthma, is a reason to deal with the mice this week rather than over a month.

Keeping mice out once they are gone

Nothing you can smell or plug in keeps mice away for long. What keeps them out is closing every gap of about 6 mm, the width of a pencil, with metal, mortar or tightly packed steel or copper wool, because mice chew through plastic, rubber, foam and wood. Peppermint and ultrasonic devices are the usual hacks people try, and the evidence for both is poor.

In an Auckland house the mouse-sized gaps are usually in the same places: where the pipes come through under the kitchen sink, behind the dishwasher and in the laundry, under the garage door, around cable entries, and at subfloor vents with the mesh missing. University of California guidance notes that ultrasonic sound has very limited use against mice, because it travels in one direction and does not reach behind objects, and that mice soon get used to a repeated sound. The materials and the places to check are set out in full in our guide to rodent proofing a house.

When to stop doing it yourself

Stop and get help when you are still catching mice after two to three weeks, which means a supply from outside and a gap still open; when there are droppings in more than one part of the house or in the ceiling; when the house is a rental, a food business or a home with a baby or someone with asthma; when you find gnawed wiring; or when something has died in a wall.

We look for the gaps as well as the mice, and every inspection ends with a written list of the entry points and what will close them. You can have the house treated and the gaps found, or request a visit and tell us where the droppings are turning up.

Questions

Questions about mice in the house

How many mice are there if I see one?

No reliable multiplier exists, and the sighting matters less than the signs: droppings in several cupboards and a nest mean an established group, while a few droppings in one corner may be a single newcomer. Mice breed fast, with five to ten litters a year of five or six young according to University of California guidance, so treat one sighting as a reason to start trapping now.

How long do mice stay in a house?

Indefinitely, if food and shelter are there. Mice do not need free water, since they get enough from their food, and they do not move out with the seasons. They go when they have been trapped out and the way in has been closed, and not before, which is why the gap matters as much as the traps.

Are house mice hard to get rid of?

A few mice in a kitchen are not, if the traps are plentiful and set along the walls where they run. They become hard when the gap they use stays open, or when the house backs onto paddock, bush or a reserve with a constant supply, and that is when trapping on its own turns into a routine rather than a result.

Do mice come out during the day?

Mostly at night, but a mouse seen in daylight is not unusual, and University of California guidance notes that they are active whenever food is available. Daylight sightings together with a lot of droppings do suggest a larger group, though, and are a reason to set more traps rather than fewer.

Should I use poison for mice inside?

We would rather you did not in the living areas. Mice seldom travel far from their nest, so a poisoned mouse usually dies inside the building, often in a wall, and loose bait is a risk to children and pets. Use traps first, and if bait is used at all, keep it in a secured, lockable station well out of reach.

How do I clean up mouse droppings safely?

Open the windows for 30 minutes first and wear rubber or plastic gloves. Spray the droppings and urine with disinfectant or one part bleach to nine of water until wet, leave it five minutes, then wipe up with paper towels and bin them. Never sweep or vacuum droppings. If you become unwell afterwards, see a doctor and mention the exposure.

Sources

If you need someone

If the mice keep coming back

Rodents

Rodent Control

Auckland has three urban rodent species and they behave differently.

Read about it

More advice

Other things worth knowing

Identification