Rats in the house: the signs, and how to get rid of them

Signs of rats in the house

The clearest signs of rats in a house are droppings 12 mm or longer, grouped along a route; dark, greasy rub marks where fur brushes against beams, pipes and skirting; gnawing with tooth marks about 4 mm wide; food taken from the pantry or the pet's bowl; and running or scratching after dark, heaviest in the first half of the night.

University of California guidance adds signs outside that are worth a walk round the section to look for: droppings near pet bowls and feed bins, burrows under the compost or the rubbish bins, nests in the firewood stack or behind boxes in the garage, and rats running along power lines or the tops of fences at dusk. In a long-running case there is also a sharp ammonia smell from the urine, and somewhere quiet a nest of shredded insulation, paper or fabric.

Gnawing is the sign people underestimate. Rats gnaw because their incisors never stop growing, so a rat living in a house is chewing all the time, and it chooses whatever gives its teeth an edge: the corner of a skirting board, a plastic pipe, the sheathing on a cable, the lid of a food bin. If you are not sure a run is still in use, a light dusting of talcum powder across it overnight will show footprints and tail marks by morning, a check University of Florida extension guidance suggests.

How many rats are there if you see one?

There is no reliable number, whatever the internet says, and the multipliers that circulate are not backed by any study we can point to. What tells you more is the evidence: droppings in one spot suggest a newcomer, while droppings in several rooms, a well-worn run and rats seen in daylight suggest an established group, and rats breed fast enough for the first to turn into the second within a season.

The breeding figures explain why. University of California guidance puts the average female Norway rat at four to six litters a year, weaning twenty or more young, and ship rats at three to five litters of up to eight. Rats are mostly active at night, so one seen in daylight usually means a population large enough that some animals are foraging outside their usual hours, or a nest that has been disturbed.

Rats in the roof

Rats in the roof space of an Auckland house are almost always ship rats, the climbers also called roof rats, arriving along branches, fences and power cables and getting in at the eaves. They will not leave on their own while the roof gives them warmth and shelter and food is within reach, so the fix is traps on the top plates and the runs, then cutting off the route up.

Nothing a roof rat hates will move it out for long. Rats shy away from a new smell or sound at first and then get used to it, so what works is physical: branches cut back well clear of the roofline, gaps at the eaves and along the ridge closed, and the downpipes and cables that reach the roof checked as routes. In a roof space with old insulation the nest is usually in it, along the edge nearest the eaves.

If you are still not sure what is making the noise above you, our guide to telling a rat from a possum or a bird in the ceiling goes through the timing, the sound and the droppings.

How to get rid of rats in the house, in order

There is no overnight fix, and nothing safe kills rats instantly indoors. The fastest real result comes from doing five things in the same week: work out which rat it is and where it gets in, take the food away, set enough traps on the runs, check them daily and recover every carcass, and seal the entry once the catches stop.

Identify. The droppings and the height of the activity tell you whether it is a ship rat in the roof or a Norway rat underneath, and that decides where everything else goes.

Take the food away. Food goes into sealed containers, pet bowls are lifted at night, rubbish goes in bins with lids and the compost is closed, which is where Health New Zealand's advice starts too. It is also how you bring a rat out of hiding: not by chasing it, but by leaving the bait on the traps as the only food on its route.

Trap enough, in the right places. Traps go flat against the walls and along the beams where the droppings are, baited but unset for the first few nights if they are ship rats. We do not recommend loose bait from the supermarket anywhere in the living areas of a house.

Check daily and recover. A trap that has caught something stops working until it is emptied and reset, and a carcass left for days brings flies and a smell. Gloves on, double-bag it and put it in a lidded bin.

Seal once the catches stop. Close the way in with metal mesh, sheet metal or mortar rather than foam on its own. Which materials hold and which a rat simply chews through is set out in our rodent proofing guide.

When to stop doing it yourself

Stop and call someone when there is activity in two parts of the house, the roof and the subfloor or the walls and the roof, when fresh droppings are still turning up after two weeks of trapping, when rats are seen in daylight, when there is a smell of something dead, or when you find gnawed wiring. A property on a reserve, gully or stream edge, with a steady supply next door, usually needs more than a householder's traps.

If you rent, who pays for rat control in a rental usually comes down to how they are getting in. Otherwise you can book an inspection and treatment, which ends with a written list of every entry point we found and what will close it, or request a visit and tell us what you are seeing.