Why do rats and mice come indoors in autumn?
Last reviewed by Dan Burn, RSPH Level 2
Short answer
Rats and mice come indoors in autumn because they do not hibernate. As temperatures drop and food outside runs short after the late-summer harvest, warm homes with easy food become the best option. They breed fast. A female brown rat can have 6 to 8 young every six weeks, so a few in October can become many by winter.
Do rats and mice hibernate?
No. The British Pest Control Association says rats and mice do not hibernate and are a problem all year round. What changes in autumn is where they choose to live.
House mice live in buildings all year. Brown rats and house mice also breed all year, so there is no winter pause in numbers.
Why do they move indoors in autumn?
Late summer is easy for rodents. Harvests and warm weather give them plenty of food and cover outdoors.
As temperatures drop and food gets scarce, rats move towards houses and indoors. Wood mice, often called field mice, look for warmer places to nest. A dry loft, a wall cavity or the space under a kitchen floor is ideal.
Many homes around Stoke Poges and Farnham Royal back onto fields or woodland. That puts them right next to where these rodents spend the summer.
How fast do rats and mice breed?
| Brown rat | House mouse | |
|---|---|---|
| Young per litter | 6 to 8 | 5 to 6 |
| How often | Every six weeks | Up to 8 litters a year |
| Can breed from | About 5 weeks old | About 6 weeks old |
| Breeding season | All year | All year |
A female rat can become pregnant again within 10 to 24 hours of giving birth. Pregnancy lasts about 21 days. That is why a small problem in October can be a large one by Christmas.
What happens through a typical year?
Every year is different, and weather shifts the timing. This is the general pattern.
| Month | What rodents are doing | What to do |
|---|---|---|
| January | Rats and mice already indoors keep breeding | Check lofts and under sinks for droppings |
| February | Indoor activity carries on | Fix any gaps you found over winter |
| March | Wood mice start breeding outdoors | Clear garden clutter and wood piles |
| April | More food and cover outdoors | Check sheds and decking for burrows |
| May | Outdoor breeding continues | Keep compost bins free of food waste |
| June | Gardens and fields give plenty of cover | Use catch trays under bird feeders |
| July | Plenty of food outdoors | Check the base of fences for runs |
| August | Late-summer harvests give food and cover | Book any building repairs that affect walls or pipes |
| September | Temperatures start to drop | Proof the house: the main month for sealing gaps |
| October | Food gets scarcer. Rats head indoors and wood mice stop breeding | Set traps at the first sign |
| November | Rats more often seen in daylight as they search for food | Bring bird food in at dusk |
| December | Rodents use warm places to nest | Keep food sealed and check the loft |
What should you do in September and October?
Autumn is when prevention pays off most.
- Walk round the outside at ground level. Look at pipes, air bricks, door bottoms and the base of walls. A rat needs only a 15mm gap, and a mouse needs much less.
- Seal gaps with wire wool set in quick-setting cement. Then check higher vents and gaps.
- Clear wood piles, rubbish and overgrown corners next to the house.
- Do not overfill bird feeders. Use a tray to catch spilt seed and bring feed in at dusk.
- Make sure bin lids close, replace cracked bins and bag food waste.
- Store cereal, pasta and pet food indoors in sealed containers.
- Check the loft, airing cupboard and under the kitchen sink for droppings. Our droppings guide helps you tell rat from mouse.
When should you call someone?
Call as soon as you find fresh droppings or hear scratching at night. Acting early means fewer animals to deal with. Our guide to getting rid of mice covers DIY first steps.
We treat mice from £139 and rats from £149, including VAT, with 2 visits each. We call back within 30 minutes, Monday to Saturday, 8am to 6pm, and agree a fixed price on the phone. Visits are usually [same or next day].
Questions people ask
Will the mice leave in spring?
Usually not. House mice live in homes all year round, not only in winter, so they stay unless they are removed and the gaps are sealed.
Why am I seeing rats in the daytime?
Rats are more likely to be seen in daylight in autumn and winter, when they are searching harder for food and warmth. A daytime sighting is a good reason to look for burrows and droppings.
Do field mice come into houses?
Wood mice, often called field mice, are unusual indoors except in winter. As the weather gets colder they look for warmer places to nest.
Is a mild winter good or bad for rats?
Bad for you, good for rats. The British Pest Control Association says harsh winters used to keep numbers down, and mild winters have helped populations grow.
How many young can a pair of rats produce in a year?
In theory, a pair of brown rats could produce up to 200 young and 2,000 descendants in a year. Real numbers are lower, but it shows why acting early matters.
Sources
- BPCA warns of second spike in rodent activity (British Pest Control Association)
- Rattled by rats: PestAware advice sheet (British Pest Control Association)
- Living with rats and mice (RSPCA)
- Differences between mice and rats (Lewisham Council)