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Rats and mice on Sydney's hottest day: why dry heat drives rodents indoors
Today is the hottest day of the year so far in Sydney - around 32C with a dry north-westerly wind - before a cooler, showery change arrives tomorrow. Hot, dry weather is exactly when rats and mice start moving indoors: outdoor water sources dry up, and a home with a dripping tap, a pet bowl or a garage full of stored food looks very attractive. Here is what changes and what to check today.
The rodents found in Sydney homes are usually roof rats (Rattus rattus), Norway rats (Rattus norvegicus) and house mice (Mus musculus). Hot, dry weather changes their behaviour: outdoor water puddles, moist garden beds and surface moisture disappear quickly, and rodents start actively looking for water and food near buildings. The dry north-westerly wind also carries scent further, which is part of why activity can suddenly become noticeable on a day like today.
Why a hot, dry day drives rodents indoors
Water is the main driver. On a 32C day, rodents need water to regulate their body temperature, and the usual outdoor sources - puddles, damp garden soil, condensation on plants - dry out quickly. A house offers consistent water: dripping taps, leaking pipes, air-conditioner condensate, pet water bowls, laundry tubs and toilets. Food follows: pet food, open bins, stored dry goods, bird seed and compost all become more attractive when natural food is scarcer. The cooler change tomorrow does not end the problem. After a hot stretch, a showery day with cooler temperatures sends rodents looking for shelter as much as food and water - which is why a combination of removing water, sealing entry points and dealing with any established population is the practical response this week.
Rodents can squeeze through gaps of around 6 millimetres. Finding and sealing the entry is usually more effective than relying on traps and baits alone.
What to check
A hot-day rodent check covers both water sources and the places rodents shelter.
Indoors: behind and under the fridge and stove, inside cupboards, under sinks, in the laundry, storage areas and garage, and around hot water services.
Above and below: roof voids, ceiling cavities and subfloors - look for droppings, gnaw marks, grease smears along wires and pipes, and shredded insulation or nesting material.
Outdoors: pipes and downpipes, air-conditioner condensate lines, compost bins, rubbish bins, pet food and bird seed, garden sheds and piles of stored material against the house.
Signs: droppings (rice-shaped for mice, larger and darker for rats), scratching or scurrying sounds at night, gnaw marks on food packaging and wires, rub marks along skirting, and pets becoming restless near particular walls.
Photograph what you find and note where. That record tells a technician where the population is active and how it is getting in.
Remove water and food
While the heat lasts, removing what attracts rodents is the fastest way to reduce pressure.
Fix dripping taps and leaks, and wipe standing water from sinks, tubs and trays.
Do not leave pet water bowls or food out overnight, and store pet food in sealed containers.
Keep bins sealed and emptied regularly, and manage compost and bird seed so they are not accessible.
Store dry goods, pantry items and garage-stored food in sealed containers.
These are daily habits rather than one-off jobs, and they make the property a much less obvious target during the hot stretch.
Seal entry points
Rodents enter through gaps that look harmless. The practical list includes:
Gaps under doors, around garage door edges and roller door seals.
Holes around pipes, cables, vents and air-conditioner lines where they pass through walls.
Eaves, roof edges and any gap between the roofline and fascia that leads into the roof void.
Subfloor vents and gaps around the slab edge where rodents can enter from underneath.
Sealing is most effective when combined with professional treatment of the existing population - otherwise rodents may simply find the next gap.
How treatment works
For a contained problem, snap traps placed along known runways - along walls, behind appliances, in roof voids - can work when checked daily. This year, changes to retail rodenticides in Australia mean common supermarket rat baits are being withdrawn, so professional rodent management is increasingly the standard approach. A licensed technician identifies the species and the active areas, places traps or bait in tamper-resistant stations in the right positions, seals entry points and plans follow-up visits, then confirms when the population is controlled. Bait and traps need to be positioned where children, pets and non-target wildlife cannot reach them - another reason professional placement is worth it.
When to call for help
Call a licensed technician if you find droppings in multiple areas, hear activity in the roof or walls, see gnaw marks on wiring, or if the activity continues after sealing obvious gaps and removing water and food. In an apartment, townhouse or shared building, rodents can move through shared walls, risers and roof voids - let the technician know the building type so treatment is coordinated rather than confined to one unit.
RODENTS IN YOUR HOME?
Text your suburb and where you have noticed activity.
Tell us whether you are in a house, apartment or townhouse, and what signs you have seen - droppings, sounds or gnawing.