Rodent call-outs across Hertfordshire roughly triple between mid-September and the end of November. It's the single most predictable seasonal pattern we see, and it's driven by two things: outdoor food running out as harvest ends, and night temperatures dropping below the point where mice and rats can comfortably stay outside.
The house mouse
House mice can squeeze through a gap the width of a biro lid — around 6mm. In October they push hard against every weakness in the building envelope: airbrick mesh, gaps around waste pipes, worn garage-door seals, holes where cables enter. Once inside they breed fast: a female can produce a litter every three weeks through autumn and winter, kept warm by your central heating.
The brown rat
Rats need a slightly larger entry — around 20mm — but they're stronger and will gnaw soft mortar, plastic and timber to enlarge a gap. The most common autumn entry points are damaged drainage runs, broken air-brick covers and the gap where the kitchen waste pipe leaves the house. A rat in the cavity wall or under the kitchen floor is far more destructive than a mouse, and the gnawed cable risk is real.
The proofing that actually works
- Walk the perimeter on a dry October day and look at the building like a rodent would: any gap, any rust hole, any unsealed pipe penetration.
- Pack large gaps with stainless steel wire wool before sealing with mortar or silicone — rodents chew through silicone alone in days.
- Replace worn garage and shed door brush seals; this is the single most common mouse entry we find.
- Cut ivy and climbing plants back at least 30cm from walls and roofline — they're a ladder to the eaves.
- Check the drainage: lift inspection covers and look for displaced rodding eyes or broken pipework, the classic rat motorway.
If you've already heard scratching in the loft or behind the kickboard, proofing alone will trap them in. A combined treatment-and-proofing visit removes the existing population first, then closes the entry points behind them — far cheaper than chasing the same problem all winter.