Brown rat: the field card
The rodent of cellars, courtyards and sewers, and how to shut the door on it.
Card 01
Rattus norvegicus
In short
The brown rat (Rattus norvegicus), also called the Norway rat, is the big urban rodent: 20 to 28 cm without the tail, active at night, living at ground level, in cellars and sewer networks. Its urine can transmit leptospirosis and it gnaws through cables and ducts. Lasting control combines secured bait stations with sealing the routes it uses to get in.
Brown rats live right next to us. They dig burrows in courtyards and banks, travel through sewers and come up through pipes, service ducts and unprotected basement vents. Strong swimmers, they can slip through a gap of barely 2 cm.
They are wary of anything new in their surroundings, a behaviour known as neophobia, so traps set in a hurry are often ignored. Effective treatment starts by reading their routes: where they eat, where they drink, where they pass.
Tell-tale signs of brown rats
- 1Spindle-shaped droppings 1–2 cm long, grouped along walls or near food.
- 2Dark, greasy smears low on walls and around corners, where the fur always rubs.
- 3Burrow holes at the base of walls, under paving or in flower beds, with freshly turned soil.
- 4Gnawed ducts, bags or doors, and scurrying or scratching at night in partitions and false ceilings.
Risk index
DeratiseurPRO rating, from 1 (low) to 5 (high).
- Health
- 5/5
- Damage
- 5/5
- Spread
- 4/5
The risks
- Leptospirosis: the bacteria are shed in urine and survive in water and damp soil. Since August 2023 it has been a notifiable disease in France.
- Contamination of food and surfaces by urine and droppings.
- Gnawed cables: outages, short circuits and fire risk, plus damage to insulation and pipes.
- Fast breeding: sexually mature at 2–3 months, with several litters a year.
How we treat it
- 01
Detect
We map droppings, runs and burrows, inspect drains with an endoscopic camera when needed and chart every entry point.
- 02
Neutralise
Secured, locked, anchored and numbered bait stations with an approved rodenticide, or mechanical traps where bait is not allowed.
- 03
Lock
Steel wool and mortar in holes, mesh on basement vents, non-return valves on drains and tight door sweeps.
- 04
Monitor
Follow-up visit, bait-take records, removal of bait at the end of treatment, photo report and written guarantee.
Prevention checklist
Simple habits that lower the risk of the intruder coming back.
- Use lidded bins and never leave rubbish bags on the ground.
- Don't feed pigeons or cats in courtyards: leftovers draw rats in.
- Fit basement vents and air bricks with mesh smaller than 1 cm.
- Clear out cellars and plant rooms to remove hiding places.
Frequently asked questions
Rat or mouse: how can I tell?
Look at the droppings: 1–2 cm and spindle-shaped for a rat, 3–6 mm for a mouse. A brown rat has a heavy head, small ears and a tail shorter than its body; a mouse has large ears and a tail as long as its body.
Is the bait dangerous for my dog or cat?
We only use locked, anchored bait stations that children and pets cannot open. If you think an animal has swallowed an anticoagulant rodenticide, call a vet at once: there is an antidote, vitamin K1.
Why do rats come back after treatment?
Because the entry routes were left open, so other rats from the network move into the empty territory. The Lock step is what makes the difference: we plug, mesh and fit valves where they were getting in.
Got brown rats at home?
Price shown before you book, 2-hour time slot, same-day photo report and written guarantee.